I agree that MSR (or other brand) fuel bottles for use with stoves should not (MUST not) leak, since they are designed to work under pressure from the stove. Even if the bottle were topped up full and allowed to get fairly hot from sun exposure it should still hold pressure. I have two that are over 20 years old, still have original O-rings and caps, never leaked. Yours may have a small irregularity in the neck that compromised the O-ring. Hhhmmm, I just thought, I wonder of the O-rings are designed to withstand ethanol-contaminated unleaded gasoline, since the stoves are designed to burn (in the case of my old International model) unleaded, white gas, diesel or jet fuel, or straight alcohol, but ethanol-bastardized fuel is not mentioned.....?
2007 ABS Wee-Strom "The Silver Surfer"
2003 Kawasaki Concours "Mabel, the Flying Kaw"