Cadillac Repair: 1997 cadillac eldorado, cadillac eldorado, engine rebuilder

Question
can i use a synthetic oil in this engine. i was told by an engine rebuilder that it can cause too much pressure and blow the rear main seal. thank you. also your site has been especially helpful to me. i have probably read almost all info on caddys. in the overheating area the pellets worked amazingly. thanks.

Answer
To use or not to use the synthetic. If the engine was built for and came from the manufacturer with synthetic, Then YES, Use the synthetic.

If the vehicle came from the manufactuer WITHOUT the synthetic, Then use the engine oil that the engine was designed for which is the regular engine oil.