They are a piece of piss to service. What I would do is take it apart (there are videos of how to do this on the hope website) have a look and see if there is anything obviously wrong/broken/missing, give it a good clean, re-lube it and put it back together to see if it has solved the problem. Lube like this will do the trick http://tartybikes.co.uk/product.php?product_id=11151&category_id=541