I just don't think the problem is isolated yet.
It is kind of hard to believe. OK, I'll quit panicing and roll my sleeves back up and analyze this further...
Thanks Jerry. You're the second person who's suggested I investigate any electrical issues - so I'm definitely going to do that. I'm going to do some further testing before I do anything radical, that's for sure!
One thing I'll do is power the scope from a battery for a while and see if the seeing varies with other electrical loads on the AC circuit. (If it varies then it's not an electrical issue affecting the scope's tracking.)
I've got a paramount on order - it should be here soon, and I expect it will be a lot more stable. The larger Meades just can't be as stable - I'm sure you can build a fork that will hold a 12-14" scope that is rock solid, but I bet you can't build one that way that I can lift! Nothing against the meade either - like anything else it's a compromise design with inherent tradeoffs.
I thought about setting up the tripod, but I think it'll be better isolated because the feet on it are rubber. I may try that anyway.
Testing it outside the dome is a good idea too.
The most annoying part of all this is it's probably weekend after next before I can get out there again.