I used paste car wax for a long time. It worked well but still once in a while I had spots that attached itself to the metal.
Then I tried some shoe polish,,plain KIWI brand as stated above in the two piece tin.
Applied with a toothbrush & let it set while mixing up the epoxy.
I,ve never had the assemblys separate so easily since using this.
I did try plain chassis grease a couple times and it seemed like the epoxy combined with the grease coating on the parts and everything stuck together real good.
If I hadn't been in the habit of separating things after 8 to 10hrs or so regardless of the type of epoxy or release agent,,I doubt that combination would have come apart in one piece.
Everyone likely has a favorite one to use and there are many that work just as well I suspect.
But for now anyway, the show polish is mine.