You may be able to unstick a caliper, though brakes are not really the best place to be cutting corners.
Lift the front, have an assistant apply the brakes while you attempt to rotate the wheel by hand. If the right one is doing nothing (or not enough), you would get a pull to the left.
Could also be a worn steering component, like a tie-rod end on the left side. Braking might cause it to rapidly transition to a toe-out state.
Possibly control arm bushings and such, since they go under load (and toe-out) when braking. Worth checking for an alternate culprit.
Best of luck.
1986 300E 5-Speed 240k mi.