How do I determine if a slow toilet leak is due to an actual leak, or due to sweating?
Easiest way is to not use it for a while (equalize with room temperature) dry throughly, and check in a few more hours of not using it.

Teflon tape (or pipe dope) only helps on tapered pipe thread fittings. Flare and compression fittings seal in other ways, but it's not uncommon to see them taped up by folks that don't notice that.