Bought a scabby YPVS rear master cylinder off fleabay
I's in not great condition but the plunger was seized in the bore (not mentioned in description), so filled it up with WD40 and gave it a tap to move it down and clean the area and hope the spring made it pop out again
Remove the rubber boot, circlip, retaining washer and pushrod so you are faced with the cup end of the plunger. Loads of WD40, push the plunger inwards as far as you can with a Philips screwdriver. Hold the cylinder in your hand (like a grip) and slam the open end down onto a wooden surface really hard. Push the piston back in and keep repeating this until it comes out.