Hmmm!! You will first have to figure out if the problem is at the wheel, or either your master cylinder or proportioning valve.
Right off the bat, I'm ruling out the master, because only one front wheel is locking up.
Here's what I would do !! Carry a wrench with you that fits the bleed screw. Next time your front right wheel locks up and you can't turn the wheel by hand, loosen the bleed screw to releive and pressure that MAY be built up.
If after doing this your wheel is still locked, then you know you have a bad caliper.
If the the wheel gets loose, then It can only be a bad flex line or proportioning valve.