Tim, thanks for the link. A very interesting link-thread.
I have examined the Aero cap and note that all 4 relieved lobes are the same sixe, ie there is not an extra relief at the 12 o’clock position. From the thread you posted, this looks like a reasonable job. However, the new/euro style filler nozzles with the additional knurled ring would still pose a problem I think.
As for the removal of the filler ‘flapper’, again do-able, but I am perhaps edging towards the safety conscious and may thank my luck stars one unfortunate day that I left the flapper in place ( an upside down moment, yikes).
As mentioned earlier the plastic hose from a plastic jerry can has been used, albeit at slow fill rate. I have now added the high tech. wire coat hanger to my itinerary to side the flapper out of the way on new style filler pumps.
Happy filling-up !
Rob