First, make sure your mast pin is straight (I know pretty obvious). Second when teh mast is up and the pin is out look to see if you can rotate it or rake it to make the holes line up. Third, make sure that the mast base is seating ontothe mast step fully. I notice that when I raise my mast the mast base hinge has some slop in it so when the mast raises the mast base does not alwyas fully seat on it's own.
Also, you may need to make sure the mast is straight up when looking at it from the bow or stern. If your hole and pin clearance is pretty tight the mast being slightly off from vertical could cause a problem.
You can always use a smaller diamter pin. Don't go too small but you get the idea.
In the market
Previous boats owned
'74 Pearson 30
'82 H18 Magnum
St. Louis, MO