I’ve just sorted out this very problem. I initially sourced what I was told would be a direct replacement. It wasn’t! Back it went and out came the old, totally seized and corroded block (carefully drill out the rivets). Then punch out the pin from the block. Then free up, clean and grease and reassemble. The block went back in with a stainless bolt right through the mast and block at the top and two cut down brass machine screws in at the bottom, tightened against spring washers.
I’ve done about 8 hours sailing on it now with full tension on the jib with no problems. Hope this helps