My series 1 has the nobbles on the sump Also, i used the rubber gasket and it has never leaked on me!! My mate had an s1 and he fitted a cork gasket but it leaked all the time! One thing i did do was to bolt the gasket to the sump ( it came all crumpled up in a packet! ) to let it sit overnight, then glued it to the sump.Just take your time and you'll have np probs!!