• I've been using O rings to seal my headsets since 2005. They are exceptionally waterproof and only 10p each! You just need to find one, say 2mm smaller than the diameter you're trying to seal - and the trick to fitting is don't force it over the fork, simply cut it in two, seat and then rejoin with superglue which will bond it near instantly. I've had one on my Caad 8 for nine years now.

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