Seems this is the new way that older cars die off now with "electronic
problems" this one still mechanically fine at 150K miles not bit a bit
of rust anywhere, so good result all around.

I had a similar issue with the ABS on a 1995 850 T5 a few years back. I
bought the security screwdriver to get into the ECU (about £3), took it
apart, re-soldered everything and re-fitted. ABS cured, no further issues.

I think over time that the joints to the PCB-mounted solenoids that operate
the hydraulic valves may crack and re-soldering sorts them out.