Just ran across this...

All packaged beverages using aspartame have an approximate 270 day shelf

>life if they are stored at or below 85 degrees F (because additional heat

>accelerates its decomposition). This is because the 10% methanol converts

>to formaldehyde (yes, embalming fluid) in the original unopened container.

and...

"Aspartame is uniquely unstable ... as the temperature increases the ratio of degradation becomes more pronounced ... at 104 degrees for 20 weeks less than 10% of the original aspartame remained ... soft drinks displayed at a service station may reach 120 degrees." The "shelf life" of aspartame "in solution" is said to be about 270 days, IF properly stored.

Forgot to mention that Coke Light and Pepsi Max are both available at the Family Mart across from the old Klong department store in central Korat. Maybe other branches of this chain carry it as well.