Mystery leak in my loo

[RustyNails]

If the toilet base was not caulked, it could just be a lot of gunk that found its way underneath the base. Removal and a good cleaning may resolve the problem.

The base wasn't caulked, but when the plumber removed the toilet to change the wax ring, I cleaned under there on the floor. If the bottom of the loo itself needed a clean, I think the plumber would've done it. Not saying this isn't the problem, but I think he would've took care of that as he did go the extra mile on some other things.

 

[RustyNails]

It is not the vent. Is the overflow at the right height? Have you replaced the fill valve? How about a good picture of the plumbing inside the tank?

Below is a photo of the tank. All 3 plumbers and the townhome maintenance guy looked in here. That doesn't mean they couldn't have missed something (anything is possible).