"apparently"? maybe you should find out for sure what's wrong, it'd be pretty hard to "shove the plunger through the piston" - you don't want to be looking for a Grumman part, the MC should be factory GM for the chassis, and depending on the chassis model [3/4T?] a MC or kit may be available locally ..... from your picture it looks like the standard 55-59 light truck MC
Bill
