Front Caliper retracts using C-Clamp, somewhat stiff.
 

Husky did you remove the screw top , from top up tank.
Just spray the defending piston with a little wd40 and screw down on the C clamp till it goes back in . Then keep your eye on it from time to time and inspect it for leaks.Sounds like piston is sized up .Is the rubber gaiter ok on the end of caliper piston ,this stops damp getting in the bore of cylinder in the caliper.

If you have pistons on each side of calipers,once you sqeeze one back in leave C clamp attached,and use channel locks to sqeeze other one.Yes it will be stiffer.My car has four pistons,so I use the old brake pad to move in the pistons.