Just a quick question.

Hi Wjconline...

Most likely the wax gasket has failed at the base of the toilet. You'll need to shut off the water to the toilet, suck the water out of the bowl with a wet/dry vac. And then remove the toilet.

You'll need to clean the old wax off the toilet base and the pipe and then install a new wax gasket and pair of closet bolts (called johnnie bolts in my area)... see images, and install the toilet.

Any questions? Let us know...

Mark

In addition to Mark's advice:

When you say "...leaking at the main stack..." , you mean leaking from pipe somewhere ? Is it from a fitting ? Or from Clean Out plug ? Please, explain in detail...

Mark probably got it correct but I'm with Milo with this. I didn't see a complaint about a faulty wax seal but a leak in the main stack at a fitting or a joint.
Now if WJ can tell us if the leak is coming from the stack or a leak that's running down the stack it would sure help. How about it WJ, what's it doing? Tom