FWIW a rebuild kit for a mechanical caliper may not include the ramps that are press-fitted in the caliper body, or if it does they may not be easy to replace. These parts and the moving parts can wear/corrode but IME it is rare that it is so bad that the caliper misbehaves; normally new balls is enough in a BB5 or a BB7.
There are a couple of twists that are worth knowing about
1) the foot that the moving pad bears against is located by a snap ring in some caliper designs; this allows a little articulation of the moving pad. In some cases it is useful to reset the foot to one side as far as it will go so that the movement doesn't allow the pad to contact the disc when you don't want it to; the pad springs don't always push the pads back perfectly square and this can make a difference.
2) The caliper body can wear. The caliper piston is (when applying the brake at a standstill) normally supported by the ramp balls and the pad thrust; the shaft doesn't make contact with the caliper body and the OD of the piston doesn't either, (despite the offset force arising from the cable, which is higher in a 'road' caliper BTW). However when the brake is applied on the move, the pads move in the direction of disc travel and contact the caliper body, and sometimes the piston moves in a similar way too.
It isn't unusual to see some wear marks inside the caliper body from both these things. However I have seen some calipers in which the piston has worn the bore far more than the pad backings have. I think this can occur if the caliper arm doesn't return fully; this is inevitable with BB5 (because of the way it adjusts) and it may allow one of the balls to go out of position or something. A full arm return better resets the balls.
BTW apologies if this is obvious but whatever grease is on the balls ends up being mixed with pad wear debris, so becomes an abrasive slurry, and even if it is still coating the wearing parts they should be cleaned and regreased.
My suggestion is that you clean and regrease the ramps and balls (using a high-solids, high melting point grease (not copper ease) and that the FPA threads are treated with a little anti-seize, and see how you go with that. New balls if necessary of course.
With BB7 you can split the caliper and this allows you to dismantle most of the caliper without disturbing the FPA knob. With BB5 you have to remove the FPA knob because the caliper body is one-piece.
cheers