You're on the right track ;.

I've tried a wirde range og LEDs of the last couple of years and the Noflix series are one of a few that actually works in these older games. However, most of the suppliers today understand and tries to find solutions to this problem.

I'm using Noflix PLUS in all my older Bally games (Fathom, Embryon, Xenon, Centaur) and those work perfectly here. As mentioned in the above referenced article the first generation of LEDs turn on "too fast" for the older games which in many cases result in flickering.