I noticed that after a couple gallons, the reddish o-ring on the tank cap no longer seated correctly and the tank would actually leak fuel. Also, when I jumped, the truck would occasionally stall on landing, probably because the tank cap would pop open briefly. There were traces of the o-ring on the matching part of the tank and I think the o-ring was swelling and dissolving. While at the Toyota dealership, I was looking through their cheap tool bin and found a blister pack of all sizes of o-rings. Sure enough, one fit perfectly in place of the stock one and the cap closes tight and leak-proof every time now. I was worried the new one would dissolve or tear, but haven't seen any evidence of that a couple gallons later. I'm sure you could get the same blister pack at a tool store such as Harbor Freight or maybe even Lowes.