TOPIC:

I have a used rear MC for my 82 GPz550 that appears to be working, but it is full of gunk so I thought I would clean it up a bit
I also located a NOS piston and was debating replacing the old one, although if it aint broke, don't fix it is my philosophy with old vehicles
Is there a way other than using compressed air to remove the piston?
I am also wondering I were to use compressed air, what do I do with the bleed holes, just hope the pressure is enough with them open, or try to close them in some way?

Did you remove the c-shaped wire clip (retainer)?

 
 
 

I've never done it but I have heard of others using a grease gun to force a caliper piston out. I've never had a MC piston get stuck. 

I've had to use compressed air to get pistons out of calipers. Keep your fingers out of the way. 

Grease gun!  Compressed air contains a lot of energy...enough to hurt someone when the piston comes flying out.  Grease is virtually incompressible so you don't need to worry about flying bombs.

They should pop out on their own once the C-clip is removed.  There may be some crud on the barrel which is preventing the piston from coming out - clean it up as best as you can.  You could try 'cooking' in boiling water for a few minutes to loosen things up.