To check the seal of a gasket, open the refrigerator door and place a dollar bill or a piece of paper between the gasket and the refrigerator.
Shut the door, then pull the dollar bill out. You should feel tension or resistance as you pull. If there is no resistance your gasket may need to be replaced. Do this test along the entire door gasket. Also examine the door seal for cracking and stiffness which can indicate the seal needs to be replaced. This test will work on refrigerators, freezers and oven door gaskets.