As the low voltage supply caps age, they sometimes take longer to build up the voltage to the LED. Also, when the LED gets the lower volatge it seems to get stuck on dim. A simple flick with your finger nail will get it lit almost every time. Mine does it if I don't play it for a few weeks.
yeah it's not like a blown Led..for a start they have like 100,000 hour life span..it's more some sort of joint problem out side the led or something..kinda hard to say without showing you..