It doesn't come off, it is welded on!!!!!
To change the rubber seal. Tilt the machine back, to make more room at the front, and just get your hand in to put the seal on. Have patience, it's a sod of a job!!!!
To put the retaining spring back on. Put a screwdriver in the hole at the door catch. This will pin/hold the spring in place whilst you feed it on bit by bit.
Enjoy!!!!!