It sounds like you are referring to the bill transport, the mechanism directly behind the DBV-200 (or -145) head. I think there have been discussions from time to time about cleaning or replacing the transport belts, rollers, etc. You can try the Search function at the top of the page to see if anything relevant comes up. If you examine the transport you can see the gears and rollers, could try putting a small drop of light oil on each one where it turns on the shaft. If the belts are stretched or glazed and slipping I don't think there's anything that will help them except replacement. Look for grime in the path where the bill slides, clean it well but I wouldn't put any lube there as it will catch dust and stuff and quickly get dirty.
I've not seen anything about a rebuild kit being available for the JCM DBV transport. These bill validator models had their support discontinued some time ago by JCM, so any rebuild kit still sitting around would have its rubber parts aged.
You might be able to find some general purpose belts of the right size. A couple of places to try contacting for bv transport parts are:
http://www.spininc.com/https://na.suzohapp.com/Also, here is the specific area on NLG for DBV problems and discussions, there might be something there that helps with your question:
http://newlifegames.com/nlg/index.php?board=43.0You may be better off replacing the transport, there are folks here that have them available, just post a Want To Buy and you should get some responses.