I am having trouble finding replacements to my original Neil Pryde mainsail slugs. The ones that are left are the white (yellowed)track slugs with a oval ring that snaps closed thru the grommet. Hunter referred me to NP, and NP isn't responding to their on-site messaging. No phone number on the site either. I see Harken and others have permanent track cars that seem to permanently clamp to the sail. What do people use when you have to upgrade??