Ok, a little history

My DS rear brake suffered the frozen issue and was replaced (by me with stock part). After the replacement I think the brakes felt OK but I had to put the car in storage for a few years, so my memory is not that great. I pulled the car out a a few weeks ago and the brakes felt spongy and the rear brakes did not wear off all the rust from the rotors. Fronts are fine but BOTH rears are about the same condition.

I replaced the Master Cyl and bled the brake (replaced all fluid). Still spongy (and peddle goes half way to floor before really getting good braking). I even bled both rear calipers at the same time (Motive Brake bleeder).

My peddle is firm when the engine is off (pump it once or twice) and then when the engine starts the peddle drops an inch or so and becomes spongy. The peddle also drops a fraction when I put the e-brake on.

My thoughts on next steps...disassemble the rear calipers and grease the carriers (rods that connect two sides. I was also thinking of extending the caliper off the car (pressing the brake with the caliper disassembled- off the rotor) to see if it extends all the way- but I am not sure what the risks are of that...

Any thoughts?