rear end 8.8
 

can somebody tell me if the 8.8 uses a gasket on the cover? and what is the correct gear oil viscosity for it? i know it needs the modifier, and the manual states something like "ford high performance gear lube" does not list a viscosity... is it synthetic?

It sure is helpful when people state which truck they have....
 

If it's a late model F-150 with an 8.8" rear end, it uses 5.5 pts (2.7 Qts) 75W-140 (Ford P/N::F1TZ-19580-B) synthetic fluid. If it's a limited-slip, you need to add 4oz friction modifier (Ford P/N::C8AZ-19B956-A). The Ford fluid is around $20.00 per qt but is very good and readily available.

Use RTV sealant for the gasket.