Normally the OEM is not rebuildable, but it can be done by installing a Schrader valve allowing it to be rebuilt multiple times.
A few postings on the thread below for info - Caledonian Engineering & Revs Racing seem to be the places that can rebuild them. I assume both use the replacement valve technique although I might be wrong...
http://foc-u.co.uk/index.php/topic,2078.0.htmlYou could also DIY - a few months ago Practical Sportsbikes had an article on how to fit a Schrader valve, didn't look too hard
