Parking brake - again - stuck caliper

So like many others, I have had issues with the parking brakes. I've taken them apart, cleaned them and greased gear and everything and new pins.

Everything seemed to be ok, but then out of the blue, the left got stuck again. I took the wheel off, took the motor and gear off and went to turn the caliper back to release the brake. But it is stuck, as in completely stuck.

Any ideas how I can get it loose so I can move the car and get it home?

 

Have not had time to go look at it again and it is lousy weather. I'll go by again today and see if I can get it loose. It's the piston that is stuck and I have to find some way to rewind it

 

It's been sitting for 5 days now. I haven't had the time to go and try again. It's about a mile from my house, so not that bad, just inconvenient. Have other cars so we are mobile. Didn't want to call a tow truck as it has to be a fixable issue. It's a mechanical issue, I just don't understand how the piston can get stuck like that. when I cleaned and greesed the caliper I also made sure that the piston was completly smooth and clean.

 

05/2015 P85D with separate ebrake caliper

 

After trying every single tool we could think of turning the piston back and having no luck, we turned to brute force and took out the Club Hammer and hammered the caliper off. It was not for the faint-hearted, but it came off and the car is driving again. There is something wrong with the pin driving the piston. I'm properly going to get a new caliper, but I will be taking the old apart and see what coursed the failure.