Is there anything back there other than the diff that could possibly leak oil?

Adam

 

No. Bearing grease would not be oily. But there are multiple places on an IRS diff where gear lube can leak. Look for the obvious - drain/fill plugs, with worn, missing, or improperly torqued washers/bolts. Anything else will require professional attention, and $'s.

 

The diff mounts are oil filled. These have been reported to leak on a very few cars.