Courtesy of www.bmwe34.net:
1. Self locking bolts on cam oil spray bar. Look for worn camshaft lobes from this.
2. Hood & trunk gas lifts.
3. Front suspension: tie rod ends, ball Joints, possibly struts and bearings. Thrust arm bushings.
4. Sway bar links and bushings. Rear differential mount and rear subframe bushings.
5. Fan clutch on water pump.
6. Brake rotors, pads, sensors, timing belt and tensioner (M20), brake or clutch switch.
7. Exhaust components, usually muffler. O2 sensor.
8. Heater control valve, Fan speed control whether sword or resistor pack. A/C compressor.
9. Differential speed sensor.
10. Clutch, Driveshaft ujoints center bearing guibos.
11. Radiator and hoses. Thermostat.Water pump
12. Doors restraint (the metal bar that stops the door from opening too far) is attached to the very thin metal of the door frame and is starting to fatigue and crack.
13. Gauge cluster, usually capacitors repair for 5.00in parts or purchase 750.00 rebuilt unit.
14. Steering box, excessive play on center, sometimes just an adjustment.
15. Light control module (LKM) repair or replace.
16. Seat cables modified. Arm rest repair. Door panels above armrest coming unglued.Sunroof drains plugging and sunroof seals out of aligment.
17. Wheel bearings front and rear, usually front first. Sealed unit you must buy the entire hub. Cv boots on rear axles.
18. Oil canister (oil filter housing) valve is failing. This is BMW mistake. Canister needs to be changed (M30 engine only).
19. Fuel pump relay and main relay.
20. Glove box latch.
21. Excessive play in shifter handle on automatic. Adjustment.
22. Automatic transmission depending on maintenance.
23. Timing chain tensioner.
24. Fuel pump.
25. Occasionaly an oil pump. Not that common.
26. Occasionaly a headgasket. Common on M30 engine with the coolant that had not been changed every 2 years.
27. After 400k miles, you should change your engine :-)