From Bilstein Germany or a German based distributor?I'm currently waiting on my B6 front struts to come over from Germany (the rear shocks were in stock). They come with a lifetime warranty.
If from the latter, this is directly from Bilstein US when I inquired about buying from Europe:
Components purchased from or in Germany/Europe would be backed by the European warranty which I believe is 2 year limited warranty against manufacturer defect. The components would have to be returned to Europe to honor this warranty. Parts can be serviced in the US with a service cost attached. We always recommend keeping the OE parts after installing a performance suspension as they will need to be serviced at some point of your ownership, this makes the car mobile while this process takes place.
Kits purchased from the US carry a limited lifetime warranty against manufacturer defect. Wear and tear is not covered nor are dampers being used for race / competition purposes.