Freeing Pistons

My rear Pistons seems to get stuck Closed (against the rotor). they go back in once pushed but get stuck closed again when braking. Was thinking about taking the pads out and cleaning behind and trying to spray a bit of lube behind the pads,

Without getting any near the pads as lube doesnt really aid stopping.

Would that be the right way to go about it or are seals or something going to need to be replaced?

[Mod: moved to MTB Gear]