Hi Iain
I had a tonneau zip break on my 4/4 4 seater. The metal zips leak water so I went to ao a boat builder at the Brighton Marina and he fitted a plastic boat zip which had larger teath and was 99% water proof and he only charged £35. I hope this helps.

All the best

David

1997 Plus 4, Metalic Blue.
2000 Toyota Yaris. (The Tardis)