Thanks Dave,
I looked at Cherrys website earlier but couldn’t seem to see anything quite right.
Sealsdirect.co.uk also have many profiles but nothing that fits well without modification.
As soon as I posted my question I had a brainwave, looked on the Porters web-site and they list a seal/gasket for the purpose. I’ve just spoken to Ian Porter who is sending one in the post. So I hope the problem is solved.
Now I just need to remove the homemade one and clean up the channel – again.
Thank you for the suggestion.