I would start by polishing the alum. mast grouve inside and out with 600
wet/dry paper and than adding a hard silicone lubricant liberally to the
track. The slug should be a good match for the track. I have used a
wide assortment of "other-boat" sails on YUUKI to find some slugs are
off by a mico-milli and will jam no matter what! A jammed main can be a
safety hazard!
Good sailing!
Larry @ Monterey
YUUKI HMS 18 (1973)