Cover fasteners are 5/16" ... they're screws moreso than bolts.
Oil change isn't required if the condition is not compromised but it's reasonable to do so while having the transmission pulled and open. I used paint thinner as a cleaner/solvent. Best to fully disassemble the gears (except don't try to pull the main input shaft/worm gear) for access to flush all the residue. Watch for the cam bearing disc and little ball bearing in the cavity beneath it under the agitator shaft ... don't lose them. The disc should be oriented with the little dimple downward to the ball bearing.