Irrigation Well - Remove Rusted Seal

I just bought a house and 2 days after moving in the down pipe separated at the U-turn and for obvious reasons water is spraying everywhere and no pressure at the sprinkler heads. It appears that the piping was modified in the past improperly and there is only about 3/4" of PVC coming out of the elbow on the down pipe. I think this is why it separated since there is little surface area to cement them together.

The seal on top of the well is rusted and I have no idea how to get it off since there are not bolt heads. Anyone have any ideas how I can get this seal open to add a new piece of PVC below the seal and fix this?

The top of the casing is too low as it is so just cut it off below the seal. Then you can use a coupling and a section of new casing to raise it up.