You do really beautiful work, man. As menno mentioned there wasn't paint on that top lip from the factory. My belief is they knew it would eventually wear off at that point, leaving the lip surface bare metal. It may be cleared, but I bet the gas will penetrate just beyond the top of the fill where it goes inside and is very thin. These modern urethanes are so incredibly durable, but so weak when it comes to gas penetrating under it around the filler necks. It may be OK..but returning it to bare metal and sealing off an actual paint line just below that rounded top surface, erases all chances of contamination. As a fellow painter, just tryin' to help.
