This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From J.COOK@ens.prime.com (Jim Cook):
I've had properly stored engines from 1972 and 1975 work just fine.
If you suspect a motor, fire it by burying it in the ground with just
the nozzle showing, pointing up and use your launch system to ignite it
as usual. [Note: be sure and stand at least 15-20 feet away from the
motor when you fire it: Buzz]