I'm wondering if your wax seal leak is just a result of your plunging efforts to get the water to go down. I'm wondering if you real issue is that your vent is clogged. drain lines require a vent pipe usually on top of the roof to let sewer gases to escape and keep air behind the water. If that vent pipe gets clogged or blocked you don't get the air behind the water "or not enough air" which makes it seem like the toilet is clogged as it is fighting pressure for the water to go down. It is more noticeable on septic systems since it all goes into a underground tank.

When you flush does you sink or bathtub drain gurgle at all? That's a good sign you have a vent problem as it is pulling air out of the closest fixture in order to get the water to drain. The problem is that when the sink or tub does gurgle, it means there was enough vacuum pressure to pull the water out of those fixtures traps and now you have a way for sewer gas to get into the house. Anytime a drain gurgles it means something is pulling the water out of the trap.

I would either tell your landlord or just go on the roof if you can and check out the vent stack. Birds/squirrels/etc sometimes make a nest i there and can clog it up. Also leaves and whatnot from trees can clog it up also. Sometimes it works itself free and others it needs to be snaked or blasted free.