the aux fan sucks, most of the dead/dieing ones i've changed draw around 300ma when the car is off killing the battery, shitty cooling systems are old news, the new twist is the holy **** it's expensive water cooled alternator that's a bitch to change, i've had to replace every one i've ever seen and all under 100k miles, the plugs are due at 100k and really it needs them 85-90k, pcv plate is crap but hard to predict it's failure, e39 window regulators are one of the worst things ever installed on a bmw, ac compressors aren't too spiffy on any e39 but they start knocking for a little while before taking a ****, rear suspension lower ball joints suck and are not really diy, head light adjusters break and the light units bounce around inside of the light, real expensive on the later hid lights to change, the black plastic part on the abs pump will go out and need to be rebuilt, theres a couple places that do them for $2-300 and they supposedly upgrade them so they don't crap out, airbag crap in and around the seats trigger the srs light
i could go on but it's pointless, it seems the later the bmw the cheesyer they build them, however a vanos e39 540 is bloody fast so it may be worth it, but id venture a guess that it would take maybe twice the money it takes to run a e34 to run a later e39
all america wants is cold beer warm cat and a place to take a poop with a door on it