yes thats right.. the rear doors are one relay in the GM3 module.
GM3 has 4 relays and relay 3 drives both rear doors locks. thats why i was suspecting the relay as the culprit.

Also good point about the motors accumulating carbon after several cycles.

My observation about BMW in general is the motors/spinning parts in bmw are designed to be failed after some years.
Example the fuel pump failed on a highway for me last year
out of curiousity i had cut open the pump and it was baked in carbon and worn out brushes. soon after that alternator failed and same issue brushes worn out and all carbon.
Based on this observation i might still do the actuator motor.. Another great idea is to use the brushes from new motor than trying to remove the worm gear onto new motor.
I have an older lexus Rx300 than x5 and how come lexus doesn't have such wear out.
wierd ha...