[schlutzer]

Okay whoa.

Oil cooler leaks are almost always the O-rings becoming brittle and breaking. This is a 100$ fix to do yourself, very easy to do. You do not have to replace the oil cooler unless it's rusted out.

But no, your oil cooler leak is not going to show up there, it'll leak either on the axle or right on the ground.

If the flywheel cover and rearmost portion of the oil pan are wet you need to look up to the valley on the engine. 99% of the time oil there is one of three leaks, pedestal o rings, HPOP leak, or EBPV leak. All afternoon fixes and you could likely fix all three for less than 200$. I guess EBPV is off the list

To find these leaks shine a light or stick your hand under the turbo and HPOP, then go from there.

The rear main is a seal and any seal can leak, but it's very rare for it to leak.

Also are you 100% sure it's oil, not oily fuel? Fuel will dry in the warm valley in a fairly short time, but not so much as it runs down the engine and transmission out the drain hole in the back of the valley. Since you said you had an oil leak previously, fuel could be picking up a lot of oil and hard to tell the difference at a glance

 

[schlutzer]

I'm also in Ontario trust me I know the rust. The oil coolers very rarely actually rot away. And if your buddy has replaced 5 rest main seals he is one of the very few.
Absolutely no RTV on the oil cooler if that gets into the oil system you might as well kiss your engine goodbye.

You said there is a puddle in the valley, clean it and try again. There is a drain the the back of the valley that will shoe oil exactly ad you discribe

 

[schlutzer]

For every 1 guy that comes back and says it's actually the rear main, there is easily 20 that find the problem elsewhere. Rear main is also the hardest thing to check. You told us you had oil in the valley, so thats the logical starting point.

You also can't see any of the back of the block with the transmission in, the valley drain goes inside the trans as the trans case goes right up to the valley.

Sucks for you that it actually was the rear main though.