[Req:] help with rear Girling calipers

[Jens]

Hi!

One of the "unpleasantnesses" of my last post involve the rear calipers.
They are from Girling and to have a look at one:
http://home.germany.net/100-157656/temp/kolben.jpg
Now, to change the brake pads you have to turn back the piston (you know
that, I know).
By applying force and torque at the same time, this is normally no
problem.
We have done it often enough (but one slightly different Audi calipers). 
The system is pressureless and the piston can be easily turned and the
hand brake lever is easily moveable and in the "off" position 100%ly.
But there won't be more than 30mm (1,181") of opening instead of 40mm
(10mm for the disc and 2x15 for the pads).
So, my question: Is this a known problem? Can it be repaired? 
Once again: It still easily turns, but it won't move further inwards.
If you turn counter-clockwise, the opening will decrease immediately. If
you turn the right way again, the gap opens again, but in no way will
get larger than those 30mm!
Oh, on the calipers are two numbers, but now VW/Audi/VAG ones:
Girling, once 9352 and then 2619/3 

CU
Jens