I don't know if this will help anyone, but I think I stumbled across part of why my 350F was leaking oil at the head gasket. I may be completely wrong, but I replaced my head gasket and seals without worrying too much about mating surfaces and have had zero leaks. (knock on wood)
I know this topic has been beat to death, so I don't want to start a discussion on copper coating, head gasket thickness or warped heads. I'm sure all of the information has it's own merits. I just want to point out one thing to check while you have things apart. Make absolutely sure the oil flow jets that sit between the head and the block are completely clear. Then check the oil spray bars in the head that actually shoot a stream of oil on the camshaft. Make sure each hole in the bar is clear. Spray cleaner and compressed air through to confirm. Don't just do a visual inspection. Treat these parts like you would a carburetor. In my case these bars appear to have started rusting and the individual holes were getting clogged. I also noticed that some of this rust has traveled back down into the oil control jets and they looked pretty bad. I'm sure the reduced flow had to increase back pressure along the oil flow path and surely made things harder on those O-rings between the head and block.
This may not be a holy grail solution, but it can't hurt. If it doesn't solve your leak it will at least make sure your camshaft gets proper oil.
Cheers
