Try annealing your copper washers.
With the lights off in the shop hang the washers on a wire and heat them with a torch, propane is fine, until they just glow red, then you can either let them air cool, or dunk them in water, same results.
Clean them with some steel wool, or lightly file them flat, or slide them across some sand paper laid on a flat surface.
Then reinstall them after checking for burs and scratches on the banjo block, caliper, and under side of the head on the bolts.
Grigg
