Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
Apart from cleaning it like you have done unfortunately when this occurs there is nothing really else you can do from a DIY perspective that can correct the issue. There are a few problems that occur... typically it is the control board that fails however on occasion depending on the model we will see gear/belt issues as well. If you are seeing it spin but not move the disc then this is most likely.
The biggest problem here is that there are simply no service parts available for these anyway... you can't buy any internal bits.
If you want to get it fixed you would usually need to ship it out to a shop that specializes in these. Finding local low level repair shops is incredibly difficulty nowadays. I use H and R Radio Services in Pennsylvania. They take mail-in jobs and specialize in Mitsubishi radios. They do usually have a $250 minimum charge however.
For the most cost effective repair... unless this is a navigation model, your best bet is to just get a used radio that doesn't have any problems. They can regularly be sourced for $50-100.