Rear Brake Caliper Piston Not Depressing

I serviced my rear caliper pins today and changed the brake pads on the driver side caliper. I have the little magic cube to depress the caliper piston, but no matter how much I spun it, it would not depress at all. I tried to apply as much pressure as I could to help it engage, but no luck. After spinning it plenty, I thought maybe it could reverse threaded even though I was almost certain it wasn't. It started to come out even further immediately, but now it won't go back in even to the original spot.

It seems like the screw must be engaged because it backed out just fine when I spun counter-clockwise. I thought maybe there was too much hydraulic pressure to overcome and the screw jack thing might slip a little by design. I made a half-hearted attempt to relieve some pressure in the caliper (I just cracked the bolt connected to the flexible hose and let it drip a bit), but I wasn't able to get it to depress with that either.

Tomorrow, I will plan to rent one of the tools that compresses the piston as it spins it. I might also bleed some more brake fluid if that doesn't work. My next step would probably be to disconnect the caliper entirely and remove the piston (I imagine it comes out though I'm not sure).

Anybody have any thoughts? Any similar experiences? I read this post ( 2015 Prius 2 rear caliper piston won’t retract | PriusChat ), but it seems like they were able to get it with the cube which is not the case for me.

Thanks for all the help; with this and over the years of posts.

 

Today's Update:
I took off the caliper and put it in a bench vice just because I was having difficulty getting leverage. I rented the tool from AutoZone where it compresses the piston as it spins it. Because I had inadvertently backed the piston out further yesterday, I had to use the tool in some creative and unintended ways until I had the clearance to use the tool as intended. See pictures. Using that tool, I was able to get the piston all the way in. It gushed brake fluid from the fluid inlet as I depressed it.

I haven't installed it back into the vehicle yet because it was getting late, but I plan to test it quite a bit to make sure the piston is behaving properly. I was really hoping I could take it apart and see the inner workings, but I didn't want to go down that road this time around when I had gotten it to depress successfully. My working model is still that there is some designed slip in the screw mechanism, and this was somehow seized or stiff. Obviously it's not completely fixed because it never unscrews when the piston is pushed out. Maybe one of you understands something about the inner workings that nullifies this idea.

Yes, it is.

Does anyone happen to know if I can just bleed the air on this one caliber or do I need to do both rear calipers?

Lastly, I plan to replace this caliper sometime in the next couple months because I have pitting on the sliding pins and in the sliding pin chamber itself. I'll definitely disassemble the piston then and add pictures.