sounds to me like the master cylinder at the lever has bit the dust, perhaps from water in the fluid - can you see through the site glass or is it real dark?

remove brake line at caliper, if lever is now opreable and you can pump fluid out of the line, caliper piston is selzed, if it is seized really tight, I have made up a fitting with a grease fitting and using a hand grease gun, pump the piston out. now clean up parts, fine emery paper pision and caliper bore, reassemble with new boot and pistron seal. good time to clean up master cylinder now too, bleed with new fluid. I know, whole lot easier said than done. I have performed that same procedure more than once and it will work. try to find a procedure in any manual for removing a frozen in caliper pision.

Brake flushing ---

You can also do a flush with a soda bottle, and a 5 or so inch tube of airline from a fish tank (the flexible rubber kind).  Just loosen the fitting a little and push the hose on.  then open up.  put the bottle on the ground, pump away..  You don't need a friend now to flush the brakes.

I'm sure someone's thought of this or there's some kind of gizmo.  But my brother told me this trick (ASE certified mechnic, no figure!?).  Hope it's useful.

Mechanically challenged.

- Roadie

on some you can use the banjo bolt and silver solder a zerk fitting to the piece of brake line, some others, it might be easer to adapt a zerk to the bleed hole and just plug the banjo bolt with a bolt of the same thread pitch. I can't take credit for that idea, it was a hand-me-down a long time ago from a real old timer. the reason it works so well is a that a hand pumped grease gun can deliver from 5k to 10k PSI, depending on how much muscle you got. I have seen perfectly good calipers go in the trash 'cause the piston could'nt be removed. on the other hand, I NEVER seen a piston that would not respond to the hand grease gun treatment.