The passenger side caliper locks and will not release after brake bleeding?

It does sound like the brake fluid has been contaminated with a petroleum product. The definitive clue is when you get that caliper to lock up again, loosen the steel lines at the master cylinder. If you get a spurt of fluid from one of them, and the caliper releases, the contamination has caused the rubber lip seals in the master cylinder to grow past the fluid return ports and is blocking them. That's the same thing that happened to the bladder seal under the reservoir cap.

What looks like moisture under the cap is actually something else. Brake fluid loves to absorb water, and moisture out of the air. That's why it's important to keep containers of brake fluid sealed. Water won't pool or collect where it can be seen. It will mix with the brake fluid, then the only problems it causes is it leads to corrosion of metal parts over time, it speeds up the normal corrosion that builds up in the lower halves of the bores in the master cylinder, and it lowers the boiling point of the brake fluid from well over 400 degrees to closer to 212 degrees. That can cause one form of brake fade when the moisture boils and turns to vapor.

If contamination from a petroleum product such as power steering fluid, transmission fluid, engine oil, axle grease, or penetrating oil can be confirmed, the repair involves removing every part that contains rubber parts that contact the brake fluid, flushing and drying the steel lines, then installing new parts. That includes the master cylinder, the new cap seal, calipers, wheel cylinders, combination valve under or near the master cylinder, and all of the rubber flex hoses including the new one that was just replaced. Due to the wide range of loading variables, most trucks and minivans also have a rear height-sensing proportioning valve. Those have rubber o-rings, so they also must be replaced. If your vehicle has anti-lock brakes, the hydraulic controller must be replaced. If it does not have ABS, the combination valve is the junction block you mentioned. It sits on the frame rail under or near the master cylinder with the two steel lines running to it, and three leaving to go to the wheels. That valve is usually not used when the vehicle has ABS. If any part with a rubber part in it is not replaced, the contamination will leach out of it and recontaminate the new fluid and the new parts. This repair is expensive enough, but it gets a lot worse when we try to save a few dollars by not replacing all the parts at once.

The good news is most of the parts cost considerably less than they did 30 years ago. As far back as the 1980s, it was standard practice to rebuild calipers and wheel cylinders as part of a standard brake job, but today it's a much better value to buy professionally rebuilt assemblies with a warranty. Calipers in the '80s cost over $100.00. Pistons ran around $20.00 except for GM rear pistons for rear calipers. Those cost well over $100.00 each and were really miserable to bleed. Today rebuilt calipers run around $30.00 for most trucks.

Wheel cylinder rebuild kits are available, but they're not a good value unless that's all that is available. These are somewhat universal, so finding new ones isn't difficult, and they're pretty inexpensive. We can only buy new ones. There's no point in a company rebuilding old ones. In this case, you need to replace them anyway because they're made of cast iron. That's porous and will hold the contamination, then release it into the new brake fluid. You also get a new bleeder screw that's guaranteed to not be rusted tight or rounded off.

It's a good idea to pop one old wheel cylinder apart to read the size molded onto the inside of one of the lip seals. It's common to find three or four sizes are listed for one model. The difference has to do with the weight distribution due to optional equipment, and wheel base. The correct size is a design factor. It's important to install the same diameter wheel cylinders to maintain the front-to-rear brake balance.

You do not need to replace the power booster, as some people think. They do have rubber diaphragms inside them, but no brake fluid contacts them.

Let me know how this progresses.

Keep in mind the most important point is all the rubber parts must be replaced at the same time. The new calipers and master cylinder are going to be contaminated again from the stuff leaching out of the parts that weren't replaced. The steel lines must be flushed and dried too at the same time. This is why the repair is so expensive and miserable.

I shouldn't say this, but if it was my vehicle, I would be tempted to flush the new calipers and hope for the best, but I wouldn't reinstall them until the other new parts were installed.

Every year I did a demonstration for my students where I put a wheel cylinder lip seal in each of two beakers filled with new clean brake fluid. I added one drop of power steering fluid to one of them, then set them aside for one week. After that week, the contaminated seal had grown by about 20 percent and was slimy and mushy. That's what happens too in the master cylinder. The lip seals grow past the fluid return ports. That keeps the fluid trapped and unable to flow back up into the reservoir, similar to driving with your foot on the brake pedal. The brakes drag and develop excessive heat. The heat migrates into the brake fluid causing it to expand. Since it can't expand into the reservoir, it applies the brake harder, then more heat is generated.

The last part of the story that I don't usually share is after removing and washing the contaminated seal, it did shrink partway back to its original size. I still would not want to use it, but it was worth noting. The contamination is still in that seal and is going to recontaminate the new fluid.

I'm confident we know the cause of the problem. Now it's a matter of finding all the needed parts.