Morris Minor Owners Club

I had a fuel spillage problem from the filler cap so I replaced the cork gasket. This doesn't seem to help at all as it's still streaming out on every right hand bend.
The gasket is in a bit of a state. Is there something in unleaded that doesn't agree with cork? And would it be worth getting a locking cap. They are totally different - I wonder if they seal better?
Any other suggestions?

you do not want too tight a seal or you could end up causing fuel starvation due to a vacuum in the petrol tank ( i seem to recall reading somewhere )

i got a new locking type not long ago (bout 8 months) and already need a new seal

I have locking caps on both my Minors and they work fine. Make sure that you get a Minor cap so that the adapter piece fits and it is vented otherwise as said you will get a partial vacuum in the tank and the fuel pump will stop pumping.
The condition of the gasket seems to be an MOT item.