If you struggle for a seal, Log on to the AF1 forum and Pm Ken Zeller. He owns Evo and will sort a new seal for you i'm sure. They are tripple lipped so not the same as an Aprilia item.
Cheers I got mine for nix through Nick at BP132...Bike Parts I'll post up his address when I have it, he is also a UK supplier for Evo spares, nice bloke.