Tech Advice: 1980-2008 MODS?

I have a 1980 MM HD210 One*Fifty Combo. Love it.
I keep a matched quad of 'Winged C' 6L6GC's in her.
The amp has always had a pronounced hum most noticible by turning the vol. pot up (the second one from the left- just next to the bright/normal switch). I'm not a tech, but based on things I've read, I can't help but wonder if perhaps what I've got here is some sort of grounding problem?
Additionally-
1. I'm in S.CA Zip 92656 (O.C.) Is there anyone
best qualified [MM] to bring it to and-
2. A few years ago, I had a cap job done, but
don't really know how extensive it was or wasn't...
I'm wondering...
To put this amp in top working condition, what improvements and or mods might anyone suggest I
do, since it'll be on the bench anyway?
Thank you.
Marc