I have had an Xpander since they came out. I am the original owner.

I have it midi'd to my OB-8.

Do make sure the unit tunes all Ocs's.  Try out the pots to see if they move well or are "sticky" and see of they do increase and decrease the amounts of X as you turn them.  Also, check all the buttons to make sure they do what they're supposed to.  Just looking at cleaning costs. 

If you can see the unit before you purchase it, turn it on and leave it on for a bit.

Make sure the displays are not flickering "badly" and DO try the unit connected to a midi controller for proper connections.

I think you can prob find a repair book online -PDF, for the Xpander.

Good luck.  I collected many of the sounds that were being sold back in the day.

I think I still have the cassette that might have gone with it   Not sure..

Ben L.