Disassembling the top winding assembly on the 67 is a bit like unscrambling an egg — tiny pieces spring off and begin a never-ending hide-and-seek. Take it to a professional service facility. The C58 will often be the first sign of brutal wind-on treatment over time — there are right and very wrong ways to wind on this camera (e.g. wind-on in one continuous smooth stroke, with no pauses and never allow the lever to spring back to its home position).
Some repairs to the 67 can be made with TigerTail multistrand fine filament beading wire; it is very find, flexible and strong. This is commonly used today to repair the aperture coupling cord in the Olympus OM4-series cameras which, like the Pentax 6x7 and 67, also use this archaic method of aperture coupling.