I believe there's one on gnttype.org. If not I'm sure it's on the board here if you do a search. Go advanced and you can look up thread titles that way to find it.
Normally a rear main seal does not show up as oil between the oil pan and the block?
Unless you verify oil tracks, or streaks, on the front of the flexplate from the crankshaft to the outside radius, the oil is coming from another place.
Could be the oil pan gasket, valve cover gaskets, oil filter, or it could be something as simple as oil blowing out a breather and running down to the pan rail.
One thing you do NOT want to do with a turbo Buick is "ASSUME" anything without doing a complete check of all possibilities, as these cars will kick your ass if you jump blindly into them!
If the rear main seal has been replaced with the 2 piece design and didn't previously leak it's likely oil that leaked from another area and appears to be the rear main. Very often valve cover leaks or the intake manifold leaking out the rear. Crankcase pressure exposes leaks. Most won't leak till you hit WOT for a few seconds. I've seen cork pan gaskets block the slot on the girdle for oil drain back though. Careful trimming of the gasket is ok. I've seen rear seals installed backward also.
One thing you do NOT want to do with a turbo Buick is "ASSUME" anything without doing a complete check of all possibilities, as these cars will kick your ass if you jump blindly into them!