So of course as soon as you have the correct technical terms from other members on here, suddenly the search tool delivers much more pertinent results and you realize your 'unusual' central locking issue is not so unusual..
(of course, most cars' previous owners were not so cheap as to leave it until both rear door actuators were kaput..)
So I've ordered a Mabuchi FC-280PC-22125 motor off amazon, and also a Dorman actuator.
I'll see if i can fix the old actuator (excellent write up by oldskewel,
https://xoutpost.com/bmw-sav-forums/...or-repair.html but it remains to be seen my drilling skills are up to the job..)
If I manage it - I'll return the Dorman actuator. Otherwise I'll be able to fit that.
I'd like to stick to OEM parts, but I'm not keen to drop $750 on three new actuators..