Peachtree original Decco, troubleshooting balance issue

You want contact cleaner/lubricant, not just cleaner.

Best if you can take a cover off, see and get to the back of a control, but it can be sprayed or dropped around a shaft to get to a control’s innards. (tilt to use gravity). 

A compressor (shop tool or can of compressed air) can move it and aid in removing excess amounts.

You can use the small tube/nozzle attachment that comes with it, but it is a lot of pressure, it will get here and there, sometimes I spray some into a small bowl, it collects as liquid, I dip a small brush in it, ....

Rotate the control full direction several times to remove oxidation that has occurred. 

Not for slide switches or rockers, they often have materials that can be detrimentally dissolved.

If cleaning one part, it’s a good time to routinely clean them all, if feeling competent.

You can use paper, to make temporary shields for other nearby parts.

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Cleaning my vintage Fisher 500C receiver, I basically gave all the controls a bath, then used my compressor to blow the excess off. Totally noise free controls.

Temporarily protect faceplates, especially anything printed on a glass surface, like meter or tuner dials....

Sorry for the confusion re the balance control. It is indeed a Decco 1 (40WPC) but I neglected to mention that I'm feeding the amp and controlling the balance through a Wiim Ultra. 

I appreciate the suggestions so far! I'll try replacing the tube and getting some contact cleaner/deoxit. Crossing my fingers that one of these will do the trick.

So if I understand correctly one channel is slightly less than the other and you are attaining an EQUAL balance by slightly offsetting the balance FROM the source? I would either live with it or try another buffer tube as suggested above. It also looks like the version 1 uses a different value tube than the following versions. Per version 1 specs a 6922 or ecc88 is the proper tube. The new production Gold Lion and Tung Sol’s are well liked or you can try rolling some NOS stuff. I would advise since you’re using a single tube get one that’s been graded as balanced sides. Cheer’s , Mike B. 

Thank you! I definitely want a stereo signal as much of what I listen to makes use of panning/imaging/etc. I've ordered a reasonably priced 6922 and eager to see if it makes a difference or solves the problem.