problem with volume control on a tube headphone amp

I have had my headphone amp now for about 2 years and have enjoyed it with no issues, added a turntable to the mix about 2 months ago and have been using it more and more as things burn in (tube phono, new arm, new cart, interconnects) and have put about 60 hours on the system since the added turntable, about 5 weeks ago I noticed that when I turn the volume all the way down the left channel still played ever so low but still played, now within a few days it has gotten louder and now is louder when turned all the way down than I care to listen to if I was adjusting both sides myself. I was wondering if spraying some contact cleaner or wd40 into the switch/control would be a good place to start. I have the amps bottom removed and do have good access to the piece in question. The amp is a Yamamoto HA-03 and out of warranty. If this doesn't work then would the next step be replacing the volume control or is there something obvious I might be missing. The problem is on both sources, turntable and CD. Thanks for any input.