First you must make sure whatever you get is larger or the same size as yours and the profile matches.
Here is a link to the job I did
MKX-420G Front QTR Vent seals - Saloons - Jag-lovers Forums
some of the pics are bunched together, and I cant edit it
It will give you a good idea of whats involved
My old seals were original, and reverting back to a liquid, I couldnt be happier with the outcome, as it fully seals against wind and rain, and works perfectly
Cant recall where I got them, either Ebay or David Manners probably
I do recall they were about 25GBP, while the MKX items were 90GBP (and most said they had trouble fitting them)
I would be in contact with a company, I think it is CH Baines in UK, they are reputed to have the best seals