i learned the hard way that you cant replace the head unit and keep the mach 460 system. so i need to get a new factory head unit, the problem is i cant find an exact match. my factory ones model number ended in AD, all i can find are AA, AB, and AC. can i put one of those in place of my AD? i cant put the old one back in because i took it apart after it stoped working, and all the local dealerships want anywhere from 380, to $642 for a new one. please help, im taking the car to germany in a week and want to get this sorted out before i get there. thanks a bunch.