Probably the best thing to do is let it vent completely and then take it to one of those local places that exchanges tanks. Exchange it for a different tank and, if they will let you, pick one with a recent inspection date. The inspections are good for 12 years. The company that runs the exchange should find the problem when they refill it.
I just went thru this when I went to get a tank refilled and the valve was bad, and they told me to just exchange the tank. So I'm not suggesting 'putting one over' on the propane company. BTW the inspection just consists of them looking at the tank before they fill it, a visual inspection.