Given it's probably an oil or alcohol which volatilizes out of the product....and you'd be rubbing the resulting reconstituted product into a painted surface, I'd take the hit and buy fresh.
Maybe contacting the manufacturer and ask them?
When I gathered 5 half-used jars of anti-seize, Permatex told me I could use any light oil to work the lumps back into usefulness.
I'm all for saving some money and avoiding tossing any product, waxing a car is such a "pretty" job, I wouldn't want to get it wrong.