Every plastic tank I've had has swollen with 10% fuel. I first discovered it with my Centauro. The first time I took it off for service, it wouldn't go back on. I was thinking, "WTF did I screw up this time??" Literally spent hours with modeling clay to see where it was hitting. Finally realized the tank had "grown" in length. Orthodontia with tie down straps didn't do it. Finally came up with a different way of holding it down. It was still that way several years later. Rosie the Rosso Corsa developed blisters under the decals. The Mighty Scura tank has grown in length, too, but still fits. Barely. (Whew!)
Fortunately, Apoo the local Indian guy has 90 unleaded when his pumps aren't locked down. Went there tonight, but all the pumps had bags over the nozzles again. Came on home, and will wait until he pays his credit card (or what ever is happening) so I can get some more.