My understanding is if you have OEM NAV it is harder. I think I read somewhere it was possible to get a MID and add it to not lose that functionality (time & date setting, MPG computer, etc) Which I would not want to lose but as it was nit an issue for me I can't say for certain.

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BMWCCA # 480346

'72 e6Tii rip
'90 e30iC sold