Seamless Manta Flow Loop?

I'm looking to do a simple campfire scene and need a flame to do about a 3-5 second loop but I'm struggling to find a decent tutorial on making a true seamless loop. A lot of them are simply doing the trick where you take 2 renders, offset one, then opacity fade from one to the other, but that's not a true loop and you can always notice the blend point (added flame complexity, weird opacity clusters, overly hot areas from blend modes stacking). What I'm trying to find is something where you cut off the emitter, let the effect finish out entirely, then offset it on another copy so it starts at the beginning of the loop, but I can't even seem to find the loop point in the animation to know where to make that point.

I have to assume there's a way to do this beyond opacity fading, similar to how particle emitters do it.