Commando master cylinder piston

Previously andy_withers wrote:

Refurbing 72 commando. Master cylinder piston is corroded and stuck in the master cylinder assembly. I have oil for several months but the piston will not move. Will I distort the cylinder assembly if I heat it up in the oven or with a blow torch? The aluminum should expanding more that the steel?

I would heat gradually in an oven, then allow to cool slowly after removing piston