I've seen this issue mentioned more frequently around the web of late and I've suffered from it for a while myself. One of the prime symptoms is pulling the handle and having it go vertical with no resistance. You can then ratchet it a few times and it will sort-of work normally.
Several years ago, I did a complete suspension and brake detail (off the car) and found one of the parking brake caliper levers had frozen. I put the caliper in a vise and got on the lever with a large pair of channel-locks square and in-plane. I was able to break the actuator lever free and work it thru the full range of motion, then reinstalled everything. It was better for a while, but has been problematic again lately.
I just did a seasonal flush of all the old fluid out of the brake system, then pulled the rear pads and rotors off one side at a time. I used a medium set of needle-nose pliers to engage the 2 retractor holes in the piston face and ran the pistons out until the dust seal just began to unseat from the piston groove. I sprayed cleaner inside it and gently twisted the seal a bit to make sure it wasn't stuck. I turned the piston back into full-retracted position, then cranked the hand lever a few times to extend the piston. I next sprayed silicone lube inside the boot, then spread some silicone grease in the seal groove with my finger and screwed the piston back down flush again. I manually screwed the piston out and in about 10-12 times to insure the mechanical screw mechanism was working freely. I greased the floating caliper slider pin a bit and pulled the caliper back and forth several times to make sure it wasn't binding. Lastly, I spread a small dab of silicone lube on the face of the piston where it contacts the inside pad, then reinstalled the rotor and pads. I moved across the car and repeated the process again.
I've driven several times since doing the work, and the parking brake handle and self-adjusters seem to be working better than they have in 15 years or more.
