How old is your boat, is the track anodised aluminium or stainless steel?
With an old boat the problem is often finding if the correct aluminium track and plastic insert is still in manufacture, it often is not.
If the aluminium track is distorted or crushed the old and plastic insert will not pull through.
Firstly try Sunseeker and see if they have any or a record of what it was and who supplied it.
The main UK manufacturer going back a while was Wilks but Sunseeker may have bought it in from US or Europe in the day.
Some years ago I had a Fairline 36 with damaged rubber and track that was crushed as well as damaged, I had the old removed and a new one fitted it was the only answer as the old track and insert was out of manufacture.