Ah OK, so it is the switch leaf that pushes the roll over back up, there is no spring as such.  the washer is no problem, the little clip may be a bit harder to source, hopefully it is hiding in the cabinet somewhere.

The lower clip on the roll over will come off with some gentle prying.  From what I can see it is basically what limits the upwards travel of the button...the lower the clip on the stalk of the rollover, the higher the roll over protrudes from the playfield.

Yep, that's it in a nut shell. Unfortunately the bottom of the cabinet is pretty clean so I don't like my chances of finding it. I think it's long gone.