Toilet in the master was a bit on the wobbly side, and had been since I moved in. I assumed it would be the classic case of a broken flange, but when I removed the toilet to examine the situation I discovered that this was not the case at all.
The flange was in great shape, so what was the issue? Digging a bit deeper...
Of course, it's not screwed down to the floor, because there is no floor there. No doubt at some point the subfloor had got a bit of rot in it and apparently they cut it out and didn't bother patching it back in properly when they redid the bathroom. Instead they filled the gap with spray-foam insulation. Brilliant.
Luckily there was a floor joist under the missing part of floor, so it was a simple matter of filling the conveniently sized 1.5 inch gap with a few bits of plywood.
That gave a solid enough base to screw the flange in, and then all that was left to do was install a new wax ring and drop the toilet back into place.
Good as new and rock-fucking-solid. Eventually I'd like to replace the flooring in here, as the laminate wood flooring is just the wrong material for the job in a wet area like this; the MDF backing soaks up water like a sponge and breaks down really quickly. I'll likely replace it with tile, but that's a job for another day.