So, tore the motor open again today. Rings and bore were not the issue. Ring end-gap is spot on, cylinder bore itself is great too. Looks like the MLS head gasket gave up. Had coolant and oil all over every layer of the gasket, and the head showed some scorching marks around the firing ring area on the exhaust side. Don't know how this is possible, but the pressure in the engine cases still seems really high. Apparently it's not exhaust slipping past the rings, like I thought. Piston skirt looks fine, not scorched at all.
Where else could exhaust be making its way into the cases? Between the steel gasket layers and into the timing chain tunnel, but not into the coolant passages like before?
To top it all off, it looks like it was burning a lot of oil, too. The dome in the head, exhaust runner and valve face were both coated in sticky black gunk, none of which was there when I tore it apart the first time. It cleaned off with some effort, but I don't know how that oil was making its way in there anyway...Intake valve and runner looked perfect.
Any ideas, folks?? I'm dying here, waiting for new head gaskets to arrive in 2 weeks...:facepalm: