normally if seal sump gasket and still have oil leak there, its gearbox out and rear oil seal has failed behind the flywheel big job, would pay to do clutch at same time and gear box input shaft seals and bearing..
if you loosen off all the bell housing bolts by 5mm all way around you can lever the gearbox away from engine block and seen inside behind the flywheel there should be no oil there if is them oil seal failed,,, also if leaking might want to check end float on crank shaft as if mains get worn this will make the oil seals leak as well
Yeah, check out a video I recorded when I pulled off the oil pan below. When I was looking behind the flywheel, it looked like there may have been some oil in there. However, it wasn't a lot and with a leak like this, I would expect a lot more oil if it was coming from the rear mail seal. Plus, I would imagine that if the leak was coming from the rear main seal, I should see some kind of flow of oil coming from this area right?
Here are some reasons (that may not be true) that it isn't the rear main seal.
1. I didn't see a flow of oil from the transmission when I pulled off the oil pan
2. There generally isn't much of a buildup of oil in there
3. The clutch was replaced in 2016 before I bought it. It was done by a local Mini mechanic here in Atlanta. The paperwork doesn't mention the replacement of the rear main seal, but, wow, if it wasn't done, he would have to be the biggest idiot in the world.
4. A friend mechanic told me that rear main leak is a pressure leak, meaning, it only leaks when the car is on. This leak comes when the car is not on at all. It litterally just seeps out without the engine running.
Video link: youtu.be/SY-VmKOLWvg
Any thoughts would be great! I may be completely wrong! I wonder if this is just a defective oil pan gasket??