My friend's gears are shot. 3.42s in his 95 Z28.

I havent taken a look at it yet but I wanted some ideas on what to look for.

Last time i was under his car i noticed oil crap infront of where his pinion seal/drive shaft area... But it was sprayed up..?? When i had a leak there is just dripped down..
Perhaps his pinion seal broke, emptied his oil out and which caused the failure.

What all parts could have been damaged do to running no oil, the auburn differential, gears, anything else?

I'll look for broken teeth too since he says on each rotation theres a thumping/clunking.

Also Does anyone know of a link that shows how to properly install gears and set the lash?