MKIV failures are relatively uncommon. The fact that you have 3 potential MKIV failures points to something else that is probably going on. Maybe you have a bad antenna or bad antenna cable. Or, maybe your car has some electrical issue that is causing problems.

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input