What chemical would you soak a master cyl in?

4spdragtop said

Same deal going on here, stuck valve....
Soaking in all sorts....parts washer, MMO, stuck valve is going to be fun....
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Some thoughts on this................

Pumping grease in through the front outlet might press it out?

Weld a tap to a rod, thread it into the valve and use a slide hammer weight to pull it out??