Thanks for being there to help me to diagnose the
possible source of this leak (before I take the toilet
up).

I have a leak from the underside of a new toilet
installation. By looking thru a small opening in an
adjoining room, I can see water dripping from the
underside of an elbow in the cast iron drain line.

This elbow is directly under, & about 10" below the
toilet. Since there's 6 feet between me & the drain, I
can't see exactly where the leak originates. Although
it seems unlikely to be leaking from there, it almost
appears to be originating from the oakum/lead joint
between the top of the elbow & the drain pipe. I am
however certain that it's not from above the floor
level.

I recently remodeled this bathroom.I installed a new
ceramic tile floor and toilet. Because the old floor
flange was broken, it was replaced with a two piece
iron flange that incorporates a rubber compression
seal. It seems very unlikely that it's leaking from
that joint.

The toilet seal to the flange however, is a large
molded rubber ring that seals under compression between
the flange & the toilet underside. On the advice of my
plumbing supplier, no wax ring was used; only the
rubber ring. My gut feel says the leak is probably
from this joint.

Complicating all of this however, is a lack of a solid
mounting of the toilet on the floor. Something is
warped so there is a slight rock to the toilet that
bolt tightening doesn't cure. Question, what are the
best type of (preferably tapered) shims to use? I tried
wood shims but they soon gave out & the rock returned.
You say to use pennies, but their thickness isn't
always suitable. I've heard plastic fails as well. Do I
dare use something like Rockite expansion cement that
will flow & mold to fill the gap? I doubt very much
that any caulk will work.

What do think may be causing this leak & how do you
recommend I try to fix it?

Best regards, Dick