We've had our '17 GLS 550 for coming up on 5 years now, and there's always been a small oil leak towards the back of the engine that very slowly drips down and around the lower oil pan. I had Mercedes re-do the lower oil pan gasket and also check out the rear main seal when the tranmission was out (to fix a/c refrigerant lines that go to the back of the car) and the rear main was fine. The leak seemed to be coming from somewhere up higher, but we could never figure out the source and it still is there, but I don't worry about it because it's such a small leak (none ends up on the garage floor).

Fast forward about two weeks ago when I was doing another oil change and I noticed that suddenly there's some fresh oil leaking from the front end of the engine. It's ending up on some hoses at the very front and dripping onto the bottom engine cover. Again, I couldn't source the leak.

Then a few days later I was watching Alex from Legit Street Car's recent video where he bought and is fixing up a GLS 63, and he found that the "oil thermostat plug" was leaking. Video here -
Do the non-AMG engines have this same setup? I'm wondering if this is the source the leak on ours. Seems crazy to me that they would use plastic for this and a huge o-ring that is going to eventually just fail.