The MKIV assessment anecdotally comes from reading hundreds of posts across a few of the prominent BMW navigation forums. MKIII failures are very common. We see a lot of those due to power loss at the wrong time. Spontaneous MKII failures are becoming a little more frequent, but still well below the norm. The only significant MKIV issues seem to be weak lasers, but even those are generally constrained to people trying to use copied DVD map disk. Other hardware failures on the MKIV only comprise a tiny fraction of combined MKII and MKIII failure posts I have seen.

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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