a few of my optimum things separate, and cause no probs once agitated.
the pink metal polish, the optimum protectant plus...but they are easily shaken before use for uniformity. all of my buffing chemicals from them are in opaque containers so i can't observe separation, but i have some stuff as old as early 2008 and once shaken it has performed perfectly. i think the smaller poli-seal bottles are clear i guess, and allow the user to observe separation easily.
i would not be worried about it separating permanently unless it was exposed to freezing or other temperature extremes. i think separating from sitting is totally normal and doesn't change the emulsion, so therefore agitation will combine the naturally separating components without issue. i might be wrong, but that's what i've found from experience.