How do you actually get it to mix? I have tried to make the mixture and as soon as I stop stirring it the two separate again.[/quote]

I’ve not had that problem. Plain ordinary NAPA auto supply automatic transmission fluid and acetone brought at a local hardware store have been used. I mix and keep it in a small glass jar with a lid. An old baby food jar was handy, so it was used.

The ATF is the real stuff, not a synthetic blend. Could that be a factor? Another might be the vessel used to mix and store? My guess is at least some plastics might react to some of those?