Well, as I fear the Permatex I have on hand isn't going to cut it - its for threads (so great for those little screws). I have a feeling the o-ring kit I have back in Texas would likely have something that would work. So instead, tomorrow morning I'll get some regular Permatex regular RTV to smear around the gasket / glass / divots on the tank.
I dislike messing with this sight glass!!
I guess I should search around the forums on "bing sight glass" too...