I used to be an authorized service agent for Maglite before they pulled all of their service center contracts - the biggest issue with the old-style maglites is heat dissipation along with reflector design. The original mags were designed for incandescent bulbs and there's not a lot of places for the heat to go. The original maglite LED retrofit bulbs had to have a thermistor that would back off the current when they started cooking themselves and had poor reliability. As a result, maglite re-engineered their switch and bulb assembly along with a new reflector that has been optimized for LED's.
Just be aware of this when choosing LED retrofits - simple bulb-size drop-ins will have a poorer beam pattern with a donut shaped hole in the middle or have poorer reliability.
The LED retrofits can make an old light usable again, however just be aware of the limitations before spending too much money on them. $32 gets you a new maglite, but they're still under 200 lumens. Modern Fixed-focus lights typically beat out maglite in terms of brightness, and the focusing function is no longer needed because there's at least 5-10X the amount of light.