try the o-rings if that dosent work then its ur cup seal. i have seen them on ebay for 20 buck but ive also been told another markers cup seal will work too the type escapes me at the moment. but be patient and one of the wiser members of mcb will chim in and help u out, im sure.
The loudest sound in the world is a click.... when you were expecting a bang.
Non-Projectile Master Painter