My father's hobby is lapidary and he has several tumblers. I was wondering if I could disassemble the rejector and use one of his vibrating tumblers to dry polish the parts similar to bullet casings. Any opinions?
Sounds like a lot of work considering the parts you remove and polish are not even the parts that are giving you problems. The coin path that needs cleaning is on the body of the rejector which you won't even be dumping into a polisher.
You have a common problem, don't turn it into a complex one! Follow the suggested simple steps first.