Another brick wall trying to remove steering wheel collars

It actually looks like someone has tried this before. I have tried a pik and a screwdriver down the side but it seems frozen.

If I press down on the whole assembly, it forces the shaft up a half inch or so. In theory, should the disk not be able to be pushed down the disk to reveal the pin ?

How important is this disk ? Would I be better off to take the grinder to the side so I can pry it off ?

Sorry for all the questions..I know this should be easy.

Thanks
ian.