If you test it at a piece of sheetmetal, you will easily find out, if it's still good. It must dry completly, give a good surface and adhere to the metal.

If it was stored unopened in a good place (cool but not frozen)it is probably still good. You may add some solvent thinner if some has gone.

After all these years having a 440 I realized that this means having an attitude... and a budget.