Originally Posted by racebum

good job

research royal purple with this car though. it's a PAO based group 4 base stock with no real seal modifier or at least not one that works. PAO base stocks shrink seals and can harden them. amsoil has a nice seal additive pack in their PAO oils if you like PAO, i just have personally seen more c5s develop leaks with royal purple than any other oil ever. on a new car it takes a long time for this to happen. on one the age of the c5 it may happen in just a couple years of use.

redline is a group 5 ester oil and actually by nature swells seals. mobil 1 high mileage also has a seal conditioner added to what's more or less a very refined group 3 base stock. these are my two favorite oils for older high performance or air cooled applications....they just seem to leak the least. redline also has an extremely high ZDDP level. great for high cylinder pressure, air cooled or full blown race engines

rather than debate pros/cons of various base stocks the seal angle on a c5 is one that's worth paying attention to simply because of the age