Mystere 5.5 Mast ball bushing

Hi all,

I bought my first beach cat the other day and one of the principal problems I'm working through is the mast step bushing. The mystere has a cast aluminium ball and a cast aluminium mast base, but the socket has a flat top, which means the normal hobie 16 cookie doesn't work.

Does anyone know what goes in here? Mine is worn badly from not using a bushing; I will need to build it up with the tig and grind it down.