I understand U
Mate, I understand you, altough your problem touches the limit.
I have a similar problem. Mine will play the tape for a few minutes and then starts auto-reversing and finally freezes up. After a while it switches to radio broadcasting but the tape will stay stuck inside.
I took the unit to a car audio repairer (R's in Tottenham, London - UK - good one) and the guy took it apart (literally), changed the tray mechanism, motor, the works, and found out that the chip that controls the Mode switching is damaged.
He searched all known suppliers and sources but could not find the damn chip. Would you freaking believe it?
I need to test the unit with a Grundig MCD46 6 disc CD changer and if it works I'll be sorted as it'll only cost me £199.99 (vat & pp inc) at www.caraudiodirect.com. Better that than a new head unit which the Fiat Dealer Desira in London will sell for £399.99. It sucks... I could buy a head unit + cd changer for much less than that.
If you live in London maybe you should try R's. They will run diagnostics and will advise you on any costs before proceeding.
Wish I could be of more help.