Thank you William, eloquent as ever....

Funnily, I had just joined MZriders, to pick their brains on just this.
My searches however, did not bring up that page. Interesting.
I would rather buy a seal kit however, than a whole new petrol tap. I mean, I already have two...!!
However, after building it up with the old seals, from the non-leaking spare tap I have (despite them being hard, and initially leaking) by this morning, the tap was dry....!
Yippee!! One presumes they have swollen once setted again. But this will not I fear be a permanent fix.
Universal Acerbis tap on its way. Just to have. For when this leaks. 17 quid, sitting on my shelf, for years!!
Cheers
a