Gaskets are sold separately, unless you buy the whole light fixture with cord. Since your light was working recently, there's a good chance it's just the bulb that went bad. Whenever you open the fixture to replace the light, you should always put in a new gasket. However, if you're just putting the old dead bulb back in until your new one arrives, it's probably ok to put the old gasket back on. Just don't turn on the light to be safe. Definitely order a new gasket though with your new light.