This more than likely has nothing to do with the purple led.

Gaines manual tells you to clean the bill acceptor with rubbing alcohol. This also happens to be the one bill acceptor in the ICT portfolio that you cannot do that very action with. My guess is that the clear plastic in the bill path of the bill acceptor is now white.

Unfortunately there's not much you can do except get the parts replaced. Its not a cheap repair though.

My personal recommendation is to see if a stacker unit can fit in your machine and replace the P70 with the stacker unit, be sure to get one that supports MDB. MDB is a industry standard interface so any bill acceptor supplier should be able to help you.