85 300TD Turbo:
I was changing the front brake pads last night and discovered that after replacing the inner pad on the r/f caliper the outer pad was having trouble coming out. The outer piston is stuck. The caliper is a Girling or Bendix not Teves. I finally got the pad removed and tried to compress the piston w/o luck. Both pads are worn evenly. What could cause the piston to seize other than rust/dirt? A friend suggested an "airlock"? The caliper shows no signs of leakage. Should I try bleeding the system?

Thanks for your time.

Alec.