A few years ago in NZ there was an issue with a batch of fuel imported from Australia... it caused all sorts of mayhem with various fuel system components failing -from memory, fuel lines, pump diaphragms and other components were susceptible to degradation from use of this batch. I don't recall all the details too clearly now, but it may have had something to do with the addition of ethanol to the fuel -I'm sure others will have a clearer recollection and provide the accurate info...
Point is, this batch was refined in and sourced from Australia. Leads me to believe there is or was at least some AvGas refining ability in the West Island.