If you don't open the air-tight seal, can last quite long. Perhaps 2 years or 3 years tops? If opened, it's oxidised and exposed to moisture. I wouldn't keep that too long. Maybe can use it as flushing oil.
A fellow Skyline owner asked me if there was a gathering coming soon. I didn't know how to answer him. It's almost the middle of 2010 and perhaps it's about time we organized a gathering for the year.