Thanks dude for wishing me luck, those pistons/rebuild kits are surprisingly expensive, ran into this with another bike, a kz1000, high price point for what reason, maybe they have to be highly-precision machined to fit in the m/c bore, or maybe its a high-failure-rate item that yields them a nice revenue stream. The kz1000 also had a stuck m/c piston like this cb900c.
Getting the hard-stuck master cylinder piston out of the m/c bore of the kz1000, well that took me a bit of fumbling around on the kz, I came up with this approach for that bike which I'll use on the 900c -- the old 'tap-as-m/c-piston-puller' trick:
