Boy, does this one hit close to home. A few years ago I found a 47k mile, 2 owner (they were best friends, so kind of 1 1/2 actually
) no-hit no-paintwork totally stock 1996 Porsche 911, even had the "unleaded fuel only" peel off decal still on the gas gauge. Only thing not OEM, a $79.00 POS Sony head unit, the CDR210 had crapped out 2 months prior and the seller had "the shop" put it in. Of course they pitched the original unit
.
Upon choosing the correct Blaupunkt aftermarket unit that looked much more like it belonged there I removed the offending Sony to find exactly what you did. I was beyond livid, no recourse though so I sat back, drank a beer and got over it.
As has been noted, best off to snag an OEM stereo harness and spend some quality time on your back like I did. Post a WTB ad in the Parts Section if no luck with the prior mentioned members.