The stock CD player in my '97 GTS didn't work when I got it. Here's what it did: Any time I turn the ignition on, the player tries to eject a disc, even if no disc is present. When I try to insert a disc, it will not suck the disc in, doesn't matter if the radio is on or off. If I push a disc in, it won't play, but still ejects ok. Any time it ejects, the ejector mechanism click multiple times. Here's a video showing exactly what it was doing:

I think I've found the problem. Maybe anyway. I had the CD player section out of the radio chassis(only 4 screws hold the CD player assembly into the radio chassis), and I made a discovery. The bottom of the CD player has three ribbon cable connecting the bottom circuit board to the rest of CD player. When I pulled them out of their housings, I noticed that there were little dents in the contact surfaces. From the digital speedo in the Mighty Caprice™, I know that this can cause all sorts of odd behavior. The way these contacts work is there is a spring loaded "finger" that presses on the cable contact pad. Over time, the spring tension can dent the cable, making contact spotty. I wiggled these cables around a bit, and reassembled everything. Low and behold, it works! It's been a month now, and it's still working like it's supposed to.  If it goes wonky again I've got a technique for filling in the little dents that I'll try out. Here's a pic of the bottom of the CD player section. You can see dents in the cable. All three of the ribbon cables have similar little cable dents.