Just went thru this on my son's 95 e34 530iT (with 110k Km on the clock)
The symptoms were the same as what you are experiencing. The motor and regulator were the originals (regulator riveted in). disconnected the electrical connection to the motor and using a multi-meter determined that I have voltage and the switches worked etc. Keep in mind that both (console and door) window switches need to be in place to test.
Before replacing the assembly (at least here in Canada the pass/rear motor isn't available separately) I figured with nothing to lose I removed the "magnet can" which is held on with qty 2. T25 screws and this exposed the armature and motor brushes. I found that I could rotate the armature by hand ( you could see that the regulator would move "very" slowly) indicating that the worm gear was ok. I did remove the motor brushes and then remove/clean the armature, lube and reassemble using contact cleaner on the motor brushes . I did find reassemble of the armature a bit of a pain as the shaft is going into a blind bushing you end up with a "air trap".
Reassembled the "can" also made sure the window regulator slides we free and clear, lubricated (the existing lube was dried out and somewhat hard).
With the door card off I attached the door window switch and applied power to the motor - I had success!
Now while I removed the armature and brushes to clean - reassembly of the brushes was a bit of a pain as the springs are small - easy to drop and as well the "clip" is plastic - in hind sight if I had to do this again I'd try the contact cleaner on its own first before taking the brushes and armature out but the commutator is somewhat hidden.
Hope this is somewhat helpful..