while that seal leaking is not impossible, its far from common.
usually, its oil from the weep hole (at top of pic) from overfilling, or someone over greased the splines in the pic. them splines need very little grease on them, unlike the splines at the other end of the final drive assy.
but, to answer your question, I have never had one apart. they are similar to a differential in a car, in that great care must be taken on reassembly to get everything just right.
another option would be to purchase a used one with good input splines (like I said, leaks at that seal are not common)
Last edited by michiganteddybear; 03-05-2015 at 04:29 PM.