Back at this - during the summer, I typically ride by bike alot, and my company had gotten a contract with a really large ($$) customer that needed alot of attention. So, no work done on this during the summer.
Yesterday, I fired this amp up and the fluctuating offset is gone. I didn't do anything to the amp itself - I did rewire some of the power circuits at the bench as I had way too much stuff on that circuit. Basically, my electronics bench, the kitchen and a few other outlets including the one in which I have a little electric heater hooked up (for winter) and about 4 fluorescent . I'd blow that breaker occasionally.
So now, the electronics bench is on it's own circuit, no electric heater, no fluorescent lights, no kitchen. But really can't put things back to see if that fluctuating offset comes back.
When powering up the unit, I had also found my grounding wire had come unhooked for the amp board, which is unbolted so has no mechanical ground. Again, I'm not sure this plays into the funky offset - it's just something I learned and always do - if I break a mechanical ground, I generally run a wire to keep that path intact (our equip at work is fussy about such things).
So, my offsets were running about 27mv and 38mv. I wanted them to be close to the same - installed a pot in series with a resistor (I didn't have just the right size pot) on the left channel and just adjusted it until it was close to the right channel. Both around 27mv now
Here's a short video of results (if you can see it - it's on G+)
https://photos.app.goo.gl/zAy6TXw8ZDL5K2rO2