Not sure what you are referring to here, if it's a covered humbucker then replacing the polepiece screws if they are rusted up, and metal polish for the cover, if the plating is a bit shot though, replacement is necessary if the look is important to you. That goes for a Tele neck pup cover also. If a strat pup, well if the cover is dirty, windex and a clean cloth, maybe 409 or similar cleaner first for tougher grime, either that or replace them. For scratched up non covered HB, or soapbars, well I have taken fine wet dry carbide sandpaper to the tops of them (also cleans the poles up a bit), getting finer and finer,good to have a shop vac handy sucking off the sanding debris as you go along. Polishing compound and cloth.Then cleaning with some cleaner and a cloth. You'll never really get it down to a stock finish, but if you have one that's badly scratched up it does make it look nicer, although it changes the colour a bit, I took a black bobbin and did this, and I stopped before getting into fine-fine grades, and it looks kinda greyish/black like a piece of slate rock ... kinda cool. Although, I suppose you could somehow colour it with something. Stratdeluxer'97 spoke one time of bobbin toppers, those might be a viable option also, and someone spoke one time about colouring new strat covers to be vintage looking, maybe there is an opposite approach that can be done as well ...bump....