I think it's fixed finally. Got home from our vacation and ordered the fifth master cylinder for my kid's car, and it's working
.
To recap:
first one: Centric 36283 - the piston wouldn't return to rest
second one: Raybestos 36283 - same issue; returned it to Amazon and got another
third one: Raybestos 36283 - weak piston but worked; leaked in the rear
fourth one: MBM - $79 and cap and bale were painted black (like a rebuilt); rear brakes locked up
fifth one: Centric 36283 from Classic Industries $45 - seems to work
Thanks to all who offered advice and encouragement.