I got the car a year ago and I have done 3 oil changes. From my first change, while tightening the plug I felt that the resistance is not increasing as expected. I did not continue to turn the ratchet. I had the same situation on the next 2 oil changes but now I get a couple oil drops leaking on the floor. I believe that the drain thread is on its last legs. I believe that a technician overtightened it and initiated the thread damage before i got the car. I have been tightening oil plugs in MB aluminum pans for 20 years and I have always been careful so I don’t think I caused it. Regardless, the damage is done.
Initially I was thinking of removing the pan and repair the thread with a Helicoil or Key locking insert. After spending time on WIS I realized that the engine would have to come out. Hendrik mentioned that the PO of his damaged engine had to break out the rear cover bottom holes to be able to drop the pan, I’m not too keen on doing that.
At this time I am thinking of plugging the drain with one of those rubber plugs and replacing them every oil change to avoid hardening. I would “weld” the drain shut and have oil changes more often considering the 1 qt. that comes out from there.
Anybody had this problem? Or some advice?

I am sorry that I am not able to offer advice on how to fix it, however, I recommend looking into fumoto valves to prevent having to keep on removing and installing the drain plug.

That being said, all the best in getting this fixed, it must be annoying.

Not a huge deal, you can helicoil/time it, grease your tap so it pulls all the metal out as much as it can. The other alternative is to drill and tap a completely different bung but I wouldn't do this because the pan is shaped to drain from a particular area to get most of it out.

The Lisle kit is nice because it stabilizes the tap. If the tap isn't dead-on the washer won't seal... that said people literally have no problem running time sert or heli in a HEAD so an oil pan ain't nothin

Rubber bung and helicoil are good ideas. I prefer helicoil. Or new pan but that is a big job.

I would not drill and tap a new hole. Metal thickness is generally thin and risks not having enough purchase for threads. Factory drain holes have properly designed local metal thickness for threads.

Have you tried a thread chaser, or is the threading damaged beyond this? If you can get the threads repaired enough to hold, you could install a drain valve device and use a thread sealer so that removal would no longer be necessary.

Speaking of which, there is such thing as a spark plug chaser, will that work?

Same concept, but the bolt thread has to be right, of course. Once the threads are cleared, an add-on drain plug such as could be installed using an RTV or PTFE thread sealant. The original plug threads thereafter never have to be disturbed.

This or fumoto valve?

Thank you all for the advice and support. I would really like to helicoil it on the factory drain. Any other place for a new drain is very risky, the pan is a cast with minimum amount of “meat” for weight savings. My concern is about aluminum chips in the pan. I would probably not use a drill because the high speed is uncontrollable and chips may fly inside. I would go slowly with the greased tap and collect all the chips turn by turn. I hope that any loose chips would be sucked by the scavenger pump and shot into the filter.
I like streborg’s amazon suggestion for drain valve. The fumoto valve may hang too low and may leave with a speed bump. Anyway that means that the thread could be salvaged by chasing.
This weekend I would place a rubber plug temporarily while a muster the courage to chase/tap/insert and gather all the bits.

I see. Good luck OP.

If you're driving hard enough to whack that valve off, you're going to break a lot of other stuff. It's fairly low profile. You'll also get a low oil warning IMMEDIATELY which is when you should shut the car off. I don't use them in principle just because I think it's a bit tacky and I just don't like counting on non OEM stuff to hold my car together.

I agree -- the plug with the built-in valve never appealed to me for the same reasons. The device I referenced several posts up is not a valve, but rather a short extension that screws into the oil pan, and has a cap that unscrews like a protective cover on a mil spec electrical connector.

Regarding thread renewal inserts like heli-coils, I think I've used only one in my life a long time ago on an alternator mount bolt that I expected would never need to be disturbed again. Does anyone know about the suitability of these inserts in an application like an oil drain plug that will be used over and over? Any chance of fatigue or wear that could lead to a failure?

Streborx, I was asking myself the same question. I have used helicoils myself several times, M5, M6, M8 but in places with very rare uses if any, like the transmission pan holes. The Key Lock inserts will definitely stay put forever but they require drilling for a M20 thread. Helicoil insert + drain valve would eliminate that problem, the repeated screwing would be moved to the valve cap.
I like this solution https://a.co/d/7SXCjeS

That's a great find, and appears to be a one-step process that chases the threads and installs a new plug simultaneously. I would go that route as a first option. IMO, drilling/tapping for an insert is as risky as drilling/tapping for a new plug size..

I used the Auto Zone rubber plug as a temporary solution. There are no leaks so far so I will leave it there for a while. There is less than 3/4 of a liter (quart) in the oil pan if the oil tank drain is done by the book. Considering that about 2 liters cannot be drained anyway, I will shorten the change interval. Compared to all other normal MB drain plugs this is about half shorter. I understand that reducing height was paramount but they could have used a thread insert. There is a higher risk for thread damage at the fastener that has the most maintenance usage performed by the most inexperienced dealership technician.

What temperatures is the rubber plug rated for?

Helicoils are good enough for spark plug head threads which hold combustion, 80 psi of oil is nothing to them. I had the machine shop helicoil an M14 headbolt before on a C63

I couldn’t find any specs for the plug rubber. If it’s the most common rubber, neoprene then max. temp. is 100C which means it’s not going to last too long.
I love inserts, where I work no aluminum thread goes without insert. I used them to repair the threaded holes in my ‘67 W111 transmission. I’m not worried about oil pressure, the oil pan bottom sees only atmospheric pressure, to my knowledge there is no oil conduit from pump shooting at the drain. The sealing is achieved by the crush washer, I wish they used a teflon washer or square section o-ring in the drain plug flange groove like the transmission plugs

I see, hope it holds up I guess just keep on monitoring.

Hmmm, I guess it is those things like if the pros outweigh the cons in a given situation, it will be worth it. Thanks for sharing.

Thank you sevenhead. I actually bought the plug I linked in post #14. There are several solutions for a valve drain. One problem is that they indeed stick out and our cars are already low against speed bumps and other hazards. My bigger problem is that my pan threads are damaged. I don’t know how damaged, the plug still threads up/down but it’s not tightening. So a permanent valve may not tighten. Mechanically, the correct solution would be an insert. Most of the inserts require enlarging the hole with a drill and I am worried that when the drill breaks through the interior surface of the pan some aluminum chips may fly inside that I would not be able to remove (even i put grease in the drill channels). I am going progressively about this: 1 - rubber plug, when this will no longer seal try to visualize the thread damage with an endoscope, 2 - find a rubber plug with high temp silicone, when this one fails, 3 - use the oversized tap/plug mentioned above, if the threads are damaged beyond oversized repair, 4 - Helicoil insert needs the smallest drill size so I will to try to tap without drilling, done slower by hand will have better control over cut chips, I will have to figure a way to remove the tang through the drain hole and make sure the crush washer is still sitting on oil pan surface to seal, 5 - single malt and cry.

Sounds like a plan to me.