As with most of the other rubber that’s been in close proximity to the fuel system, the grommet in the offside rear wing that secures the fuel filler had perished.
Removing the grommet is simple enough as the lip that sits inside the wing is quite narrow. With this teased out and the filler cap removed it comes away easily.
There was some clart round the hole in the wing – mostly waxoyl that had got through from the inside of the wing and survived washing by hiding under the grommet – but that was removed with some degreaser and a rag. As the area under the grommet would have escaped the attention of any sunlight, encouragingly there wasn’t an obvious difference in the paint colour.
Fitting the new grommet was the reverse of removal with the addition of some silicone grease in the groove that holds the wing. I found it easiest to fit the inside bottom edge first and work round from there which left the last, and trickiest, part at the outside top which has the best access.