However before I can clean it up it will need a thorough cleaning up in the parts washer. The sludge in the bottom of the caliper bore is accumulated crud from the hydraulic system, which probably has not had its fluid changed this century. The black ring half way up the bore is the fluid seal which will be replaced when I rebuild the brake, and the rusty grime at the top indicates where the brake pad has been rusting away at the edges. Horrible