...and may be different with the parking brake issue. You would need the hardware the connects the cable to adjust it correctly.
I rarely use used brake parts, but in this case, that might be the best idea.
You also could pull the caliper, drain the brake fluid and put penetrating oil in it with the piston down so that the oil will go around it. After several hours use a block of wood to keep from damaging the piston, and shoot compressed air in the threaded opening with a rubber noozle. If you can get the piston out, you should be able to use a brake hone to clean the inner surface and find a O ring manufacturer that has a petroleum resistant O ring. We used to do them all the time 30 years ago, but it became cheaper to just replace rather than rebuild. Which in your case, you can't do. You might even be able to reuse the O ring and dust boot if you are careful. Good luck...