I should be clear, the seized lever was on the old caliper which is gone and done with now, having been replaced today. The lever on the new (junkyard) caliper has full movement and appears to be working great. I was mainly mentioning it because the cable doesn't seem to be 'retracting' out fully when the parking brake is disengaged, totally regardless of the caliper's operation. The parking brake cable still moves in when you pull the lever, just not fully out.
I've seen the diagram in the service manual which shows the mechanism responsible for splitting the one handbrake lever cable into the two individual cables for each side's caliper. However, when I traced the cables back towards the front of the car, they disappeared into the underbody and I don't know where that 'split' happens to be able to take a look for an issue.
Edit: For reference, this is the 'split' I'm talking about. 04-12-2 in the factory service manual.
View attachment 229064
If your passenger side p-brake is working properly, with full movement at the caliper, then the front and passenger cables, as well as the split, are probably working properly.
The split is located under the heat shield below the p-brake handle.
When the p-brake handle is released, the factory spring on the caliper is supposed to pull the cable fully out.
(the one circled in red.)
In my case (and probably yours too, ) the boot on the cable failed, water got in and rusted everything up inside the cable.
It wasn't fully seized, it was just binding enough that the factory spring didn't have enough tension to pull the wire out, so I added the extra spring to add enough pressure to pull the cable out.
My replacement cable moved so freely, that I didn't need the second spring anymore.
I'm pretty sure that you have the same problem that I had and a new p-brake cable will fix it.
You will have to remove the heat shield to access the "split" to disconnect the old cable from the "split".
You can put pliers or screwdriver on the lever connection point on the caliper to see if you can pull the cable out fully.