CD stacker faulty

[Skateboard]

Advice re. CD player please. My CD stacker has just stopped playing. It's the original Pioneer radio/cassette/CD unit and I want to keep it and not install one of those fancy "disco" units (no disrespect). I've asked a local "auto sounds" bloke and he reckons the CD heads need re-calibrating which entails sending it away and paying a lot of money ??
My question is: are the CD changers interchangable/ compatible with each other ??
If they are has anyone got one surplus to requirement .... errmm cos they've installed a "disco" unit

[Skateboard]

Yes, I knew I wouldn't explain clearly. The cassette and radio are playing fine, it's just the CD exchanger that isn't playing. Oddly enough, it sometimes plays a few bits of a CD and then stops.
The unit is a Pioneer KEH P4500R - see below. If there's one on ebay is it just a case of unplug and plug "new" one in ??