TT600 Yamaha 1985 front brake master cylinder
 

Hi all,
the piston in the front brake master cylinder won't move, seems to be rusted in place. Trying to replace the piston but can't remove the c-ring to free up the assembly. Would consider replacing the whole master cylinder, but don't want to pay $160 for a new one, haven't had any luck finding one used. Any thoughts on how to get it apart or where I might find a used master cylinder?

- thanks