Im at 135,000 miles now on my '94 325is. Runs great, and once you get all the maintenance done its fine. All of my problems happened at 100k-120k and the car was 10years old at the time.
Things I did and you should do and/or get.
-new water pump with a metal impeller. OEM's were plastic.
-new metal thermostat housing. OEM was plastic.
-new thermostat at 120k. old one failed shut, resulting in a near overheat
-remove the fan. Install an electronic fan.
-remove rubber plug drain thing above computer. It gets clogged and results in overflow of water onto the computer
-beware of wires in the truck lid harness, many have shorted out due to disintegrated wiring. May cause fire.
-replace radiator with all aluminum one. My old one failed, the plastic water neck broke off.
-power window motor went out. replaced.
-brakes are underpowered. Replaced fronts with '04 330i rotors and calipers and carriers. Direct bolt on. Also, replace the rubber brake lines with stainless.
-front control arm bushings needed replaced. Used nice offset RTRS delrin replacements.
-trunk gasket squeaks when driving. Rub liquid hand soap into the gasket every few months.
-Oxy sensor replaced at 110k. That isnt easy to get to btw.
-drivers side door handle internals broke. Made of plastic that got brittle. Replaced.
-door panel leather was peeling off. '92-95 had bad adhesive. Replaced with new ones.
-sunroof developed serious leak. removed sunroof, replaced with carbon fiber plug. Very happy with this mod. Lost over 120lbs from the top of the car. Makes it handle a hell of a lot better.
-Shocks were shot at 120k. replaced with konis.
-Rear shock towers were shot. Replaced with Turner units.
-front towers are shot. Havent replaced them yet though.
'94 325is, '03 M3 Vert, '86 M35a2