What you do get is pressure pulsing as there is a breather from the crankcase connected to it (as well as the breather that goes direct to the throttle body) which is nominally controlled by a reed valve. Add in the amount of oil mist that is present in the air gap in the tank when it is running or just shut off and you get plenty of oil leaking from the cap if the seal isn't up to scratch. Someone (GLLOQ?? I think) did machine up a proper O-ring sealed plug for the inside of the filler neck rather than the sheet rubber pressed against the top of the filler neck which isn't a good sealing surface.
Previous Post

Last edited by RedThree; 03/07/15 07:46 AM. Reason: FOund the post and it was GLLOQ!
Calum
M3W Vol1
Vol2