Rear calipers on A6 Quattro

I'm replacing the rear pads on the above vehicle. Right rear was changed effortlessly other than having to make a tool to retract the caliper. On the left one I've trid to retract it hundreds of revolutions plus using a
large c clamp. I assume somethings frozen inside. Tiome to buy a new caliper?
Also can anyone tell me where the brake pressue regulator is on this car, a Quattro wagon 1996. The shop manual (CD by Bentley Publising. POS in my opinion)says its on the left trapizodial arm. I've looked all over the left and right without seeing it. Perhaps its only on somr models. Enlightenment please.
Roger
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Regulator is electronic most probably.\ Calipers is turn and push, only turning doesn't do the trick.
Ronald
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For the caliper, it is possible that the piston has moved so far that it is no longer engaged to the threaded piece. If you have not destroyed the threads with the C-clamp, the secret is turning with constant pressure until it reengages.
Tom
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