I am having all kinds of trouble with the rear main seal on my 2012 GL350.

Bought car one year ago with warranty and recent oil cooler seals done at dealer. Car had no issues except timing chain rattle - no oil leaks at all, completely dry. Put 5000 miles on, and had timing chain and sprockets replaced at dealer in January while under warranty.

Within 200 miles/1 week of getting the car back from the dealer for timing chain, and it was leaking oil heavily from back of the engine. Of course I suspect they screwed something up while removing the entire top end and front of engine, but they say it is not related. They are unable to determine rear main seal or oil cooler, so they agreed to re-do the oil cooler under warranty first. 10 hours later they said cooler seals were fine (but replaced anyway again). This was 2 months ago. They had the shop foreman doing all the work because the car has been at the dealer for 3 months and I have been complaining so much about the shoddy work. Guy seems very knowledgable and convinces me the rear main seal is (just coincidentally) gone bad randomly right after they disassembled the whole top and front of the engine. (yeah-right). I ask could it be the PCV valve is pinched or defective, but he says he has never seen that and no chance. But why is the rear main seal leaking 1 week after the timing chain was done?

That was early April. I approved the rear main seal job, it was done by the shop foreman in mid April and within 1 week the car was leaking again. From the rear main seal! They claim it was a defective seal and just put another seal in at their expense. That was last week. I go to pick it up and the foreman tells me it is still leaking a little and shows me the previous seal that is perfect. He used all mercedes parts and the factory tool to install.

Since the dealership is clueless, and this is the top tech at this big dealership I feel like he should know better.

So my question is, what is going on. Rear main seals should not wear out at 72,000 miles. When they do go out, it should be straight forward to fix and not continue to leak. I get the feeling the crankcase is pressurized or something else is leaking. This all started after doing a full timing chain, sprocket, guide replacement.

Any help is greatly appreciated. I work on cars all the time, first time with a diesel. My gut tells me they are missing something easy.

Thank you!

 

Where is the oil coming from? Mine 642 engine had inspection cover in the bell housing, so it should be easy to figure out the leak. Does not take much intelligence to tell difference between cooler leak, that shows on the side and rear leak, that shows in bell housing.
Why 2 replacements did not fix it? Maybe time to change the shop?

 

Leaking from the bellhousing inspection cover. My concern is that this is the second time it was replaced by the same place, and it is already leaking again in 100 miles. This is a large dealership and the shop foreman is doing the work. Now three times it is leaking, coincidentally right after all that sprocket and timing chain work? Never leaked a drip before.

Is there any chance something they did taking the valve covers, turbo, etc off?

I did test the crankcase pressure tonight - took off oil cap and there is steam coming out. On gas engines I am used to a small amount of vacuum, but this has steam and a small flow out.

 

I am surprised they replaced not only timing chain at low mileage, but also sprockets and guides. Sounds to me they like to milk the warranties. But long way from front chain to back seal, than I hear enough horror stories about repairs, that it makes everything possible.
If it is their job that fail, they have to fix it and unless you want to pay extra for somebody else doing that, I don't see any way around it.
My way to test blowby is putting a napkin over oil fill opening and idle the engine.
At this mileage the napkin shouldn't go anywhere.

 

There are a few locations that oil will drain to same location by gravity by design so investigation of topside valley area high spots should be systematically cleared first imho. The most common oil leak is CCV where it plumbs into MAF turbo intake & unfortunately that's highest up almost directly above other usual suspects (turbo pedestal, oil cooler) & a shop tech looking to quote a big job wouldn't be lying to say he/she sees oil around all those areas because CCV leak cascades directly onto them all.. the swirl-flap motor, turbo pedestal & oil cooler will all look wet & oily as a direct result of CCV dribbling onto them from above. With engine @ operating temperature, Rinse down under CCV w/ brake-cleaner & air-gun until residual oil is washed off that area & monitor to see if it comes back after a few drives. If it does, that leak must be squared away before getting to bottom of other possible suspects as to do otherwise will prevent any accuracy as to where exactly other leaks might be coming from. This would really only apply to slow oil leaks since a fast leak would rule out CCV by default right away, it's leak is a slow dribble over time but can build-up to look big if neglected or valley drain gets plugged up by debris.

 

Goes to show you mechanics now are not what they used to be. Very easy to figure it out, if he would have made sure it was all very clean. Like others say its either the seal or coming from the top and making it look like the seal. And sure glad I don't do that work on these cars for a living. Not fun fixing something and then getting blamed for messing it up.

 

Yet medical studies are in high demand.
Fact is that doctors can bury their mistakes.

 

Thank you all for the suggestions.

Background on GL350 - dealer maintained, prior CPO. Under aftermarket warranty for last 2 years.

There is more to story, but suffice it to say my car has been at the dealer since January for repetitive rework while my wife is driving brand new '19 mercedes loaners. We put more than 3,000 miles on their loaners since January and only about 400 miles on this GL350. Meanwhile all the rework is being paid for by mercedes because they are claiming failures of prior parts (oil cooler first, then 2x rear mains). I cant imagine it is not showing up somewhere in the Mercedes system as mechanic error. But I am on a first name basis with the head tech and have called two other dealerships in the area that claim this guy is one of the best (he networks with the other places). I have been under the car with the tech numerous times to inspect it. He shrugs when I ask why it keeps leaking. I have never done a rear main seal but the process on wis looks to be straight forward.

When it first leaked I suspected it was something they did during the timing chain work. Since the leak at first was so significant I decided to allow them to replace the rear main seal so they would have complete ownership of all oil leaks for 2yr 24mo (mercedes warranty). No they have no choice but to keep fixing it, and I have no choice but to keep coming back. If I go somewhere else I have to pay again.

They replaced rear main twice now and it still leaks, but much less. This is why I keep suspecting crankcase being over-pressured. It started right after the timing chain work.

I tested the CCV last night again by putting a paper towel over the opened oil fill and generally it remained in place, but moved around a bit and would eventually fall off. With oil cap open there is steady steam rising, but not any real pressure. In a gas engine I have seen slight suction on other engines. Is a diesel the same?

 

I usually buy higher-mileage vehicles and did rear seals over 20 years ago.
Seem at least MB improved rear seals so much, that now 20 years old cars with 300,000 miles still hold them just fine.
That makes me wonder, since those things don't happen, what is the mechanic experience in fixing them?
From what I remember in the past, very slight misalignment can lead to leak and those seals are tapped in with hammer, so it takes personal eye to push it right. I have no pity for mechanics as they seem to milk warranties for living.
Anyway, there is not much that can be changed at this point and if DW enjoys the rental, that ain't bad.
Good luck.

 

Dealerships repairs are a paradox because they'd much rather offer you peanuts for 'broken' trade-in to get you financed into a MY 2020 sitting on a full lot more than fix the one you brought them for repairs. Especially if yours keeps coming back to them with same issues repeatedly. Letting you hold the loaner for so long is like letting a super bluefin tuna spool out the fishing reel against drag to wear it out. Eventually harpoon, gaff, & tail noose come in form of blown deadlines for repair promise, empty excuses as to why, & repeated repair failures when they finally DO give it back to you. I've become a jaded student of the game with MB dealerships, especially if they're an AutoNation dealership in disguise.