Unsupported claim from the original poster.

Leaks at the drain seal (wax ring) are not defined by
whether there is water leaking in around it. It is indicated
by whether you're getting sewer gas around it. The presence
of sewer gas from a leak around the ring is not yet excluded.

With the design of the toilet, and the ring, it would oftentimes
be necessary for the water to go uphill to manage to leak around
the ring. But sewer gas can make its way past very nicely,
especially when the house is tight, and the furnace is pulling it in
to its air return duct. Go to the FAQ's in Toiletology at
http://www.toiletology.com/frequent.shtml

Jim Elbrecht wrote in message
...
(Marc) wrote:

It doesn't
appear to have any leaks at the drain seal, because I see no water on
the bathroom floor around it, or seeping through the floor and into
the basement.

Is there a window in the bathroom that gets tightened up in the
winter? My first thought would be to eliminate the possibility that
it is really a rear-round problem that is only noticed in the winter.

Next I would suspect the vent getting snow, debris or sitting water
that is causing a plug when it freezes in the winter.

Do you use propane gas in the house. I've seen folks confuse the
smell with a septic tank. A poorly vented dryer, hot water heater or
space heater could stink up the place.

Jim