Buy an official maglite LED buld conversion. I have a 3 D one with it in for work. It's excellent. Better than a cheap ebay bulb.
Mines been in the same torch for 5 years, it's used outside in all weathers for 2 nightshifts per week in all manner of conditions and the batteries last me 6 months at a time.
I want to keep the same torch, unless a surefire is cheaper than the maglite conversion kit?