You may from time to time find new gaskets that seem to be too small and do not fit the application. They are indeed "shrunken", having been manufactured to correct size but since grown smaller. Paper gaskets do this primarily by dehydration, loss of moisture in the paper during storage.

The fix is simple, just soak the paper gasket in water for as little as 30 to 60 seconds (thinner paper needs less time). Occasionally a paper gasket may need a few minutes soaking in water to expand enough, but longer soaking may ruin the paper, so don't over do it. Thicker paper (card stock) gaskets require longer soaking time. A gasket between two machined surfaces can be installed wet with no problem. Needing to be glued to a sheet metal cover, you may want to dry the gasket on a paper towel before trying to apply sealant.

Thick cork gaskets present a different problem. Some of these may be "rubberized" or sealed in ways that make them nearly impervious to various fluids. These will usually respond to a longer period of soaking in water, but if they don't expand in 30 to 60 minutes they likely never will.