Time for plumbing!

Hello, helpful people! Many of you know me from other hit postings such as, "Will my house blow up if I wire it this way?" and "Does that look like mold to you?" Well I have good news! I am branching out from my typical field of electrical work and moldiness and have started doing some of my own plumbing. So....
I was setting a toilet last night.I put the whole thing together (rather surprised that it seemd so easy) and started tightening the T-bolts. I noticed that they kept turning and weren't getting all that tight. So I bit the bullet and removed the toilet to see what was going on. It seems the cast iron flange separated from the cast iron drain pipe. Looking at the assembly, I don't know how they were ever connected. The thing was mightily corroded, though. Anyway that's off topic. So I went to my local Home Depot and showed the guy the piece. He actually admitted he didn't know how to fix it! And some something about being, "just the night guy. And the smart guy already left for the day."
So I looked around myself and found a PVC replacement flange with a gasket which thickens as you screw it into the drain pipe. So this replacement fits INTO the pipe while the other fit AROUND the pipe. When I put the replacement in, since the other flange fit around the pipe, there is just an empty space under the screw holes which you'd normally use to secure the flange to the floor. I was told by a family member that this is a very common occurance and that a plumber told him it's okay since the flange isn't going to come out of the drain pipe since it fits in pretty snugly once you tighten and expand that gasket.
So I believed him and completed the toilet installation. It flushes, no leaks so far. But I am worried because the toilet has a very slight wobble. So slight, in fact, that I can't even get a plastic shim under it.
Do I need to remove the toilet and fill the empty space with concrete to anchor the flange? Thanks!
-ben
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snipped-for-privacy@yahoo.com wrote:

Congrats on the new career! <g>
You're probably OK to leave it alone. The expansion flange does provide quite a good fastening.
Instead of a shim, squirt some silicone caulk in a few spots around the bowl base. It acts as a stabilizing shim and also gives good adherence to the floor.
Jim
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Speedy Jim wrote:

to cushion it.
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i had this same problem.i cut 2x4 and screwed it in between the floor joists up next to the toilet main pipe.used some longer srews to secure flange to 2x4. lucas
http://www.minibite.com/america/malone.htm
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