I posted this on another thread but it belongs here as well.
I was told on the Bottlehead forum that the only way to clean my preamp attenuators was disassembly. I had tried spraying contact cleaner/deoxit into the attenuator's weep holes and even though they seemed thoroughly drenched the scratchiness continued. As a last resort I used an insulin syringe and injected the cleaner deep into the weep holes, while working the knobs back and forth and bingo no more scratchiness. A small needle syringe will reach places that a plastic spray tube can't.