On 5/2/2012 11:30 AM, gonjah wrote:
....

... The base
of the toilet is sealed off with silicone and the holes where it's
screwed down are sealed too.

That's not good...there is no reason for and there should not be any
caulking around the base of the stool; the seal is at the flange.

More than likely your problem is there is a leak there and you can't see
it because you've forced it to stay in there and soak up the subfloor,
etc., instead of having early indications of a problem.

Take up all that caulk and I'll bet you'll find it's damp/wet.

After that, the fix will likely be obvious--take up the stool and repair
what's needed. If you're lucky it'll only be a new wax seal not a new
subfloor.

Question: On average, how often should sewer vents be cleaned out with a
sewer rooter? I've here 5 years and I haven't had it done yet. It's a
slab house.

This house is 100 yr old and has never had vents rooted out. Unless a
bird builds a nest or somesuch, what's to clog them--they're just vents
above the trap there's nothing but air.

Any suggestion on what to do next?

See above...

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