well, I've now fought the ABS failure lights on battle.
started by replacing back wheel cylinders, clean & lube caliper slides, flush all fluid and bleeding all brakes, tried not to force any fluid back thru system toward MC
Oh NO, the infamous Voodoo Red Brake and Yellow ABS were on, tried slow bleeding again
2 days of hell under the shade tree, even a cold beer didn't help.
pulled the black plastic pressure differential switch out of proportionaling valve, Ah-the culprit, coated in green-blue chunky gunk, spring and up the shaft, sticking, stuck on, cleaned and coated with light film of silicone grease, tried to clean out bore down into prop valve. who but Ferd puts a bronze spring on a stainless steel switch pin shaft?
found rear pressure side of prop. valve also full of green gunk, lost small end seal when spring drove cap out of my hand, boy is that neoprene end seal small in the grass.
all back together and bleed proport. valve, then did wheels brake bleed per Chiltons ABS section as I should have done in first place, book is right more often than old school.
RR then LF then LR then RF, cross hatch pattern, learn something new every day.
all lights off and best brakes I've had in years.
Now off on vacation

 

Hey, another story to tell your grandkids about the old Aero.