Replace it with an after market item, either via ebay or get one from:
http://www.casoli.co.uk/139/ducati-l...-cylinder.html
Yes they are expensive, but bloody worth it. You could always get one shipped from who makes them:
http://www.evoluzione.net/
If you go down the route of new seals then every time you clean the bike remove the front sprocket cover and remove any build up of chain loob. It's this and the bits of grit and crap that stick to it that cause the seals to let go. All the more reason to clean you Ducati even more! Also if you are generous with it then go easy on the chain loob.
Gareth