I bought a pair of used rear calipers so I could refinish them and do a ceramic coating on them. While taking the first one apart I may have used a bit of excessive force because I wasn't totally sure how it was all held together and when I took the piston and rubber seals off (I wanted to take everything not metal off the caliper because they'll go in the oven for curing once the coating is done), the center screw was not straight, it deviated a bit to the side. Now there is no way the piston is going to slide with the screw like this. I'm not 100% sure if it was already like this or if I caused the damage. I can move the screw around using pliers but it won't stay centered.

My question is can the middle part with the screw be replaced? I saw a snap ring at the bottom of the piston port, I'll try taking it off to see what happens.

Has anyone here even been through something similar, is that screw serviceable?
Thanks a lot in advance for any assistance you guys can provide.
Here is a pic of the caliper when I was done sandblasting it.
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I removed the unit inside the caliper, does anyone know if you can buy this little unit here seperately?