Try lacquer thinner
As I said previously, the airbrush thinner has added naphtha, which is a “hotter” solvent, and hardware store thinner is mostly mineral spirits. To each his own as far as thinner goes, but I get better results with the airbrush thinner-the use of lauquer thinner may be ok for some of you but I always fear it being too “hot”. The naphtha evaporates quicker and the paint dries faster. As long as you are paying $800-$900 per gallon for the MM paint, the thinner isn’t that much out of line. As you said, a can will last for a while! I bought two cans of it many years ago and I am about half-way through the second can!
Just look for those red label cans now instead of the old black label.
I’m NOT saying anyone is right or wrong, but whatever you find works best for you, hey go for it! The end result is what’s important!