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smilie in place of the real @
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A bicycle foot pump got mine with the other piston held in the caliper by a board and 2 C clamps to the workbench.
Not messy but to clamp it on the bleed valve had to cut the end of the hose off.
I saw this on the Moss Motoring blog recently:
https://www.mossmotoring.com/frozen-brake-caliper/
Pretty slick idea, basically block of the hydraulic connection on the caliper, fill with fluid, then use a clamp to press the free piston in, which will force the stuck piston out.
Zerk is a new word for me. In the UK these are "nipples".
Just thought you would all like to know that.