489 case, pinion seal question

In theory, if the nut has been removed and you replace it and tighten it to the factory spec of 250 lbs. ft. it disturbs the amount of pinion bearing pre-load so yes you should either replace the crush sleeve or my personal favorite is to replace it with a crush sleeve eliminator kit. That way if you ever needed to take the yoke off again it doesn't disturb anything. Search YouTube and you'll find numerous video's on setting up 3rd members

BTW: throwing theory out the window I have seen guys just put a new nut on and torque it down and it worked ok. I guess it all comes down to, do you feel lucky?