This shows the cross section of a mast step. There are only a few threads connecting the dolphin striker post to the mast step. The striker should not be able to slide thru the mast step.
If the threads of the striker are still good, then you need to replace your mast step. Push your striker post up some thru the front cross beam enough so that you can thread it into the bottom of your new mast step until they are flush with the bottom of the bowl (where your teflon chip goes). It is easier to do this before you rivet your new mast step to the front cross beam.
In this picture's case, the salt water caused the threads of the striker and mast step to fuse together over time on my 82H16 and this was the only way to separate them.