I had the the front brake starting to lockup at 70mph, when I got down to 20mph she locked solid, for the exact reason. Whatever had that stopped up, was solid. Liked to have never got it out. Took my number drill bits, I don’t remember which one, and drilled that hole a little larger to prevent that from ever happening again. Also did the rear brake and clutch master cylinder and installed rebuilt kits to each. Just FYI.