79 eltigre 6000 LC disc brake

[peter p]

My disc for the disc brakes has quite alot of play.
It moves in and out and is very close to hitting the housing it sits in.
I can also spin the disc about a 1/4 turn before it actually grabs on the shaft.
I don't see a locking screw only a key-way slot in the disc hub.

Does anyone know how to remove the disc so I can inspect it further?

Thanks