| Don't think it's dead mate...I've just had the exact same thing where my rear brake was sticking on.
I put it down to the fact that I only use the back brake once a year when I put the bike through it's MOT, I had just bled the brake to make it work well enough for that. I guessed the pistons were crudded up, through lack of use so I took the calliper off, whipped the pads out and gave it all a dose of WD40 to clean it up (obviously not the pads or the disc) and greased the pistons up with brake grease.
But mine was the same, the pistons wouldn't budge until I loosened the bleed nipple, so I just let the brake fluid come out until the pistons were back in place, then reassembled it all and bled it through again....sorted. | 
Jools
Hybrid Mode
