I just had my Muncie 318 3 speed rebuilt and was installing it last night. I had help and they were going to refill with SAE 90 but removed the top bearing retaining plug on the tail-shaft instead of the side fill plug. I snugged it back down but does anyone have guidance on how tight this plug needs to be? Does it just hold the rear bearing from moving? I don't want to drive the truck until I know I won't cause damage.

Thanks
Greg