The headlamp seals are available from Lotus, but they are a bit pricy:
|£14.17 (Feb. 2013)
The seals are made of lengths of 10mm diamater solid neoprene pipeing, superglued end to end to make a giant O-ring.
The internal diameter of this ring should be 133mm, this will then be slightly tensioned on the lip of the headlamp shell which is 143mm in diameter.
The raw material for these is available here
You can remove the headlamp shells to replace the seals without removing the wheel on an S1 - provided the bulbs are removed and you have standard ride hight shocks.