My front driver brake caliper continues to lock up

By far the most common cause is a restricted rubber flex hose. You're already way ahead of most people my observing you can open the bleeder screw on the caliper to release the trapped brake fluid. Next time this happens, loosen the steel lines at the master cylinder first. If that doesn't allow the brake to release, suspect the hose.

ABS hydraulic controllers rarely cause locking brakes. On most systems two different valves would have to stick and the problem would be there right away.

If the caliper DOES release when you loosen the lines at the master cylinder, we will have to discuss brake fluid contaminated with a petroleum product. That will be a very expensive repair, and it will cost way more to fix on a 20-year-old car with ABS than it is worth. You'd also see the rubber bladder seal under the reservoir cap is blown up and mushy. Lets hope it doesn't come to that. With contaminated fluid, both calipers would eventually have the same problem. It wouldn't take three weeks longer for the second one to cause trouble. My vote is for the rubber hose.

Rats. When the brake fluid releases at the master cylinder, that means it's the master cylinder that is trapping the brake fluid. Normally that is due to the fluid being contaminated with a petroleum product. Rubber parts used in the brake hydraulic system are not compatible with petroleum-based products and will swell up and get soft and mushy. The lip seals grow past the fluid return ports and block them.

This also proves the rubber flex hose is not what's trapping the brake fluid.

In this case there's two clues that point away from fluid contamination. Most importantly, the rubber bladder seal under the reservoir cap is still its normal size and shape. Second, the master cylinder was recently replaced. A lot of import cars have adjustable push rods coming out of the power brake booster. Those have to be checked and / or matched to the new master cylinder. Anything that holds the brake pedal down a little will keep the brakes from releasing. That includes that push rod being adjusted too long, and the brake light switch being misadjusted and holding the pedal down a little. Next time the brakes lock up, loosen the two nuts that hold the master cylinder to the booster, then pull it forward 1/8". If the brakes release, that proves the seals in the master cylinder are okay and fluid contamination is not the cause. Check if the push rod has a threaded end that can be adjusted. Also feel if you can pull the brake pedal back further than where it sits when it's at rest. If you can, the return stop or brake light switch adjustment is okay too.