Help - Rear brake calipers

[tihol_tiholov at sd27.bc.ca]

Hi, all

Car: 1988 90 Q.  (I was told that type 44 have the same exact rear
calipers).
The rear brake calipers were uncooperative yesterday while trying to put
new pads.  The piston turns clockwise forever (at least 1/2 an hour) but it
doesn't go in.  Used a pair of needle-nose plyers.  These calipers were
rebuilt when bought about 3-4 years back.  Anyone know what to do about it?

TIA
Greetings,
Tihol