Shimming a toilet

I'd not use wood shims on a toilet. They may work temporarily, but eventually water will destroy them.

What is the real problem" Rusted/broken hold down bolt?

I don't know your skill level, but pulling a toilet is fairly simple if you can pick up the weight Shut off the water and flush to empty the tank as best you can. Take the feed tubing off. Take the nuts off the hold down bolts and lift the bowl. Now you can inspect and figute out what is broke. Seal and bolts are pretty cheap.

Sometimes the floor is just not level. I had one like that and I bedded it in tile grout, then cleaned up the base with a sponge. Just be sure to use a new wax ring so you are not right back in there.

I think this is the problem. We had it come loose from the wax ring a few months ago and the plumber at the time shimmed it up but is coming loose again. So, I'd need to take take the toilet off, replace the wax wring, etc. There is no real way to shove some thing under there without messing with the entire toilet?

You can try just working some tile grout under the base with a putty or drywall knife. Keep poking it in until it won't take any more. Strike it off and clean up with a sponge when it starts to set. Don't touch it for at least a day so it cures

It is on a hardwood floor. Would the grout screw up the hardwood?

All it needed was to tighten down the bolts. They could be turned 3x by hand so I snugged them up and all was well again! Thanks to all for the assist.

Old cast iron flange rusted out on one side so I installed one of these

Oren posted for all of us...

Get the air fluff model...

Oren posted for all of us...

Whatever you do; do not get the ATR!