Terralux is out of business thanks to Covid. So their products are harder to get. I've had pretty good luck with other LED modules on Amazon.
To mercifiknow:
It's certainly fine to get an LED module for an older light. Sure, new lights are brighter, but Mags are extremely well made and will last forever. I would think about NiMH batteries in adapters, since alka-leaks will destroy a good light.
That said, Mag's newer LED models are underrated, IMO and will blow any LED upgrade out of the water. They may not be 6000 lumens, but most lights that advertise that many lumens are lying anyway. If the specs are not ANSI-rated, then they are meaningless, IMO. Plus lumens aren't everything. Beam profile, throw, and color rendering are just as, if not more important.
So, I think you should upgrade your old light, and then get a new one. Because about every 12 hours, there's a 100% chance of darkness.