Corrosion inside the socket will definitely do it. You should replace this. Cooling is an issue, and as you probably already know, you should never
let your fingers touch the reflective part of the bulb. Best to wear cotton gloves. Another serious problem which isn't generally known is that a
lot of bulbs nowadays are sheer crap. You use an ELC bulb probably. Try to find Japanese made Ushio or some older US made inventory. Lots of
these el cleapo bulbs coming out of China won't last very long at all.