Best thing is to open it up so you can actually get to the pot(s). Usually there are holes in the body of the pot so you can shoot DeoxIT into it on one side and have it tipped so the DeoxIT can drain out the other side. Exercise using a sholace wrapped around the pot knob so you can rapidly sweep it from lock to lock and then rinse with another shot of DeoxIT.
I'm not certain about this but I've found that mic pre's are the hardest to quiet and I've heard that some of that is related to the load that the pot carries and sometimes is related to flakey caps. I plan on doing a test sometime by taking a mic pre trim pot that is noisy and just replacing the pertinent capacitors and seeing shat changes there are, and also taking a trim pot that has been cleaned but is still noisy and then recapping the mic preamp and seeing if it helps.