Whatever it is, he should refurbish the entire brake, even if the problem is the brake pedal shaft.
Drum brake --- Rear brake shoes. For a drum brake, If you don't know the age of the rear brake shoes, replace them. The adhesive that binds the linings to the shoes can fail over time, so a lining can separate from a shoe, then get jammed between the shoe & drum, locking the rear wheel. It happened to me when rolling the bike of the center stand, so it does happen. I was lucky that it happened in the driveway. It would be a real drag for the rear wheel to lock at speed & far from home. But I'm guessing the op has a rear disk brake which could have other potential problems.
1981 KZ650-CSR. Competition, Sports & Road.