81 gs650g rear master cylinder jammed

[Coronet383]

1st post with a new account, probably 3rd or 4th account I've had on here. Parked the bike about 2 years ago due to electrical issues.
Just put some new tires on my 650g and while fitting the rear brake back to the rotor I had no pedal pressure. Tried to bleed it, nothing coming through. Pulled the line off the caliper- nothing. Off the m/c- nothing. Pulled the m/c and pulled it apart to find it appears the ram-rod is bottomed out in there or jammed solid.
I would like some opinions to
1- how to unstick the piston to rebuild it. (Already have it soaking in pb blaster)
2- are aftermarket/eBay rebuild kits any good or am I better off going through somewhere like OldBikeBarn?
3- would i be better off attempting to locate a used replacement m/c? No luck on this so far and it looks like the 650 had a different mounting set up.

[2BRacing]

1. Wrap a rag around the m/cylinder and apply compressed air to the fluid outlet end. Hopefully this will force the piston out. The rag will prevent the piston flying across the floor into a dark corner. I have also used a grease gun to pump grease into the m/cylinder to push the piston out, when a piston was so stuck that compressed air did not move it.
2. For safety-critical parts such as brakes, I would not recommend aftermarket/eBay parts. Rather get OEM parts.
3. If your m/cylinder bore is not pitted and corroded, it should work fine with a new OEM piston and seal kit.

[Coronet383]

I will try the compressed air trick tomorrow at work.
The local shops are trying to sell me a All Balls rebuild kit pn: AB18-1003 instead of the suzuki part. Its also about half the price of the OEM part but I can't find a decent picture of what it comes with, they are all just a stock photo that "may not depict the actual components included with the kit".