When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
It's possible that it is engine oil. I have a drip at the oil drain plug and I suppose the mess in the pictures could be oil blowing back. I change my oil topside so it's been a long time since I've been underneath without the splash shields. I've cleaned it up and, as suggested, I drive it for a few days without the shields to see what does. Both splash shields had fluid/grime buildup on them.
I should have looked closer before I cleaned it up, but the pictures seems to show red fluid on those sensors.
I usually make sure it's not oil first, a trans leak usually happens under the bell housing from the input shaft, the outputshaft at the back, or the pan gasket itself but it's always replaced with the trans fluid on these cars.
Thats probably what it is though I'd just fix that and come back. Brakleen everything clean and come back to it after you've replaced your drain plug washer
Most likely it is engine oil leaking, possibly from the rear main seal. Good luck getting that fixed, you would have to drop the transmission to get access to replace the seal. If it was transmission fluid, it would be all over the trans pan. I believe those are the cables that go to your O2 sensors, all 4 of them.
I also don't believe the drain plug washer is copper. I'll know for sure when I drain the oil.
rear main seal leak isn't usually that bad at this age. I think it's something upwind, either that drain plug which you've already confirmed is the culprit, but your oil cooler/housing gaskets are probably weeping at this age too. That ones a bit tricky since the thermostat comes out but its all doable
So, I popped off those two black covers. There was a bit of oil on the outside edges of each cover, but peering up inside the openings looks dry. I'm not going to say 100% dry, but I've had RMS leaks on my Jeep and I see nothing like that here. I've taken a couple of 20 mile drives since cleaning everything up. No new evidence of leaks...even at the drain plug. I'm going to keep the shields off for another week....if everything remains clean and dry, I still might drain the oil and replace the crush washer.
And I've pretty much ruled out it being ATF. Even so, I picked up a trans fluid dipstick and will be checking the level soon.
Related question.....what gear should the car be in to check the trans fluid level?
Park? I thought the procedure was to warm up the engine and trans fluid to operating temp, then check the fluid level while the car is running and on a level surface.
Btw, if you haven't exchanged the trans fluid before, the 722.6 loves fresh clean fluid.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
