Howard, I think that the problem is the rust on the board. It is substantial. But.....I haven't done any measuring up in the keel slot yet....Your questions makes me think I should. Possibly I will cut a block of wood to just shy of the width of the slot at the bottom. If I then attach it to a stick or something and pass it up or down in the slot it will let me know if there are narrow areas by binding up. Looking up there everything looks OK. Maybe I'll try that tomorrow. Thanks for giving methe idea. S