Previous owner changed all the framing seal on my 1978 NC33 mkII (he said it is an easy task) and left me a roll of that seal and filler
The manufacturer I was able to track down in septembre 2018 is Direct+Seal, a british company
Unit 6, Milton Business Centre, Wick Drive, New Milton, Hants BH25 6RH UK
tel : 01425 617722 firstname.lastname@example.org
Attached is a photo of a slice of that seal (in two parts, black ruber and white filler)
The seal seems to be in page 55 of their catalogue I receveid upon request.
The one that best fit the photo is CS787
Hope it helps,
PS : I have been unable to track down the manufacturer for the seal around the top sliding window in the wheelhouse.
If anyone has a hint …