As I have said before Craig I don't have any pressure build up in my tank in either direction but being older it will not be subject to the same environmental issues as yours.
This year however a couple of weeks ago when in for her MOT one of the checks was removal of the filler cap - so I wonder is it something Morgan specific or just a change in the rules.
Others in the trade on here will know.
Checking condition of seal. They did it on my bike.
