You shouldn't need to drain the diff - the oil won't be that high. Of course, if you want to change the oil anyway (which you probably should if it's been sitting, etc), then doing it prior to the job might make more sense...
Yes, if you see some rust where the seal lip is, then shine it up. Also in the bore on the diff where the seal will mate with the case (so the seal and rtv will make a good contact). Then, use some gas, alcohol, acetone, etc to wipe the surfaces down good prior to installing the seal. ALSO, pay attention and see if there is a small groove wore into the pinion shaft (where the lip of the seal was). If so, try not to tear your old seal up too bad, and compare the widths of the old and new seals. Pay attention to how far the old seal was recessed into the diff housing, and when installing the new one, you might want to not go quite so deep, if possible. The idea is to keep the lip of the new seal out of that groove... Be careful with trying to push the new seal in deeper to avoid the groove (if there is one), because you might not be able to go deep enough to miss it - and then your seal is already installed and cannot be pulled back out without tearing it up. Just something to keep in mind...
They're probably talking about elevating the rear just to make it a little easier for the worker to twist around and maneuver while under there - it's not necessary but would probably make it easier unless your rig is already lifted.
The main thing is to pay attention to the torque when putting the yoke back on - that bearing is preloaded so a wrong torque could cause premature bearing failure. Also, if torqued way too tight or way too loose, it will affect how the teeth mesh on the ring gear and cause all kinds of problems in the long run (and noise in the short run).
Just take your time and think about what you're doing when putting it back together, and you shouldn't have any problems. Good luck. <img src="/forums/images/graemlins/kewl.gif" alt="" />
