If the bubbles are forward of the filler cap, that suggests a good front brake.
Don't get the colour match quite right, and put it on with a tar brush to add to the patina.
(I once won the Concours de Tatt at the Annual Rally by, amongst other things, having various parts held on with period sizal type baler twine, rather than the modern plastic stuff.)
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.