Here's what I have noticed in my 16 years of owning BMW's
1. Do not buy 1st model year vehicles! There are always bugs that need to be fixed and parts do not hold up.
2. BMW has increased the use of plastic parts in the cars. It reduces weight and cost, but decreases longevity.
3. BMW's will nickle and dime you in maintenance. However, the big items tend to last longer than most cars.

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95 M3
03 X5 3.0
06 X3 3.0 Sport