8 3/4, (741) Pinion seal removal

Losening the nut with airtools should be no problem. Tightening however use the torque wrench. torque should be 240 foot punds when new. What's most important is that you check the preload of the pinion bearings. should be around 15-20 inch pound. If it's lower than that, keep it that way when tightening the nut after you replace the seal, because if you exceed it you might ruin the bearings.
You'll probably won't be able to change it however, because the pinion bearing preload is set using a spacer and shims which between the bearings, and not a collapsible spacer as used in the 489 casing. So if the preload is gone, which is common in a used centersection, just leave it that way, otherwise you're talking about a full rebuild (if you want to do it the right way)

Good luck,

Antoon