this is my first ls1 and I have a few qeustions about the rear main. car is a 99 formula

1. which seal should I buy?? where can I get it?

2. how should I install it, I already took the cover off, so do I need a new gasket for the cover or can I reuse it.

should I put the seal in with the cover off or should I do with the cover on the motor??

 

I just changed mine and I bought mine from bumper to bumper it was 14 dollars since all the other auto parts store want to sell you the gasket and seal for like 60 bucks I reused my gasket but just make sure it is in good condition and I put some gasket maker on it just to be safe. I installed it while the cover is off it will be so much easier just hit it with a rubber hammer that way you don't damage it.