Had a similar thing happen to my brother-in-laws BV, it would spit out the bills, he found a bunch of like new older bills and that worked for awhile but started doing the same thing again, the guy I used to get slots and parts from told me the reader was dirty and that there was no good way to clean it and gave me another used BV, that worked for a few more years and then gave out.
I believe there are some slot parts places in and around the Las Vegas area who might have a new BV that would work. You can try a google search and see what you find.
On the one we were working on we couldn't find away to take it apart to try and clean it but then it might just be it is worn out, that does happen.
Good Luck
Walt