Clogged Spray Can Tool

[metric_taper]

Darn, I was hoping you had a way to unplug the existing dip tube, as it seems that's where gravity has settled out the thick paint, and it then plugs the tube when the spray valve is depressed. But it would probably take knowing what the exact propellant is, and back feed the same (all assuming it is procurable) down the tube to clear it.
I've tried shaking the can. Even bought a shaking tool that gets inserted into a sawlzall type hand held saw. Seems once they are plugged there's no fixing them.
I guess you can't leave paint cans laying around for 30 years, even if unused, they are scrap.