2005 525 Electrical Gremlins - please Help!

[Carbonic]

My 2005 525i has presented with a bunch of electrical problems, starting a few months ago. The issues are as follows:
1. Changed front brake pads, replaced brake wear sensor and re-set indicator on i-Drive. Distance to next brake change decreases rapidly (i.e. from 40000kms to 1000 kms in the space of 1000kms), brakes and wear sensor are as new and wear sensor has correct (i.e. new spec) resistance. Have re-set followed by same behaviour 5 or 6 times now.
2. Engine overheating warning on i-Drive, no hot air from heater (i.e. suggests electric water pump or electric thermostat failure). OBD Key confirms high engine temperature. Disconnect / reconnect battery, fault corrected, coolant temperature returns gradually to normal zone. Fault recurred 3 times.
3. DSC / ABS control system failure message on i-Drive, turn signals do not reset (suggests steering angle optical sensor failure). Disconnect / reconnect battery, fault corrected.

I suspected the battery (5 years old) and had it tested for parasitic drain, load test, etc, no fault found, but replaced it anyway. No more faults for about 3 weeks, except brake wear indicator still decreases rapidly.

Latest fault: Restraint system failure (airbags, seatbelts etc). - Fault remains each time I start the car, haven't tried my battery disconnect / reconnect trick yet.

As all of the above problems (except brake wear) "fixed" themselves, I suspect a more fundamental electrical issue.

Any ideas?