I agree. Even if it is a factory unit, replace it w/ a new one. The features and quality improve as price stays the same or lowers. Just like w/ most stereo stuff. Call Pyramid if they are still around. Get a quote or estimate. Then go to Custom Sounds or somewhere like that and price around. You will find that by the time they open it, and fix it you may spend a tiny bit more for a bad *** deck.
But if it is only dirty, ouch. What is it doing or not doing?
H&H out on 290 east is a good car stereo installation and repair place. They might be able to fix it, but usually these units have to be returned to the factory for repair. If it is a high dollar unit, it might be worth it, otherwise, you should just replace it with a new one.