A bit of an aside, but if you are into DIY and thinking of spending a goodly amount of cash on a pot, there's an architectural reason these problems develop in the first place you may want to consider: wiper current.
Reputable component manufacturers usually specify whether or not
any current may be drawn through the wiper contact, or and if so, how much
should be drawn. All this depends on the type of element and wiper material used. For Cermet elements and metal wipers' it's not unusuual to see a requirement of so many 10s of microamps.
Ignoring the advice for the component used is what leads to excess noise in use. It may be that a coupling cap should have been used after the wiper and was not (leaks current through the wiper into the parallel load) or that one was, and shouldn't have been! (not enough current drawn to 'wet' the wiper)
Carbon pots in low cost equipment will always go noisy eventually, though it may appear fixable. But if you are spending the necessary for a high-quality, really well-matched stereo fader in cermet or similar, do your research to make it perform at its best. The recommendations should be in the manufacturer's datasheets