Toilet leak.. HELP!

[bigdog]

I noticed a water stain in my kitchen ceiling recently, but today has spread.
Directly above the ceiling is a bathroom.

I noticed that to the back of the toilet the floor tile is stained and damp, but not wet. I suspect the toilet wax gasket is the culprit. No hoses are leaking and the tile floor itself is dry.

I've replace dozens of toilets over the years, and always replaced wax gasket ring with new. Current toilet is original 20 yrs old, standard type bathroom version, nothing fancy. If it is the wax gasket ring, should I replace with 'standard' ring or 'jumbo' ring? What are the recommendations for use of each type?

FYI, having a plumber coming onsite to evaluate, but I may do the job myself,
since I'm familiar with the process. Still TBD, if he can do the job quick & reasonable the job is his !

Thanks for your feedback.