If memory serves me correctly, it was the once oh so coveted Cree Q3-5A XR-E.^^^Right. Though it may be something like a Q4-5A or B(A was rosier, B had more yellow). There weren't a lot of choices back then. Those tints were the first "neutrals", though often referred to as "warm". Warm whites had significantly lower flux rating at the time, as I recall(though my memory is questionable of late!).
Hate to say it, but if you've eliminated the switch, cleaned all the contacts, and tried it with fresh batteries, you may be out of options with that light.