I've heard the same thing with BMW's and M3's. I almost bought a 2005 ZCP M3, but its only fault was that it was lacking Nav. I asked about retrofitting it, and they said the same thing. I opted to buy a non ZCP M3 with nav instead (less headaches).

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James

2005 Silbergrau M3: HK, NAV, Premium & cold weather package, 18" OEM, SE Panel Filter, GruppeM Ti Exhaust
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