Its not a lot of oil but its in constant motion coming in, getting slung around and draining out the bottom to the sump. The gasket can be used over if its whole and you like taking a chance, I've done it successfully. A little gasket sealer and as said on the rubber grommet is warranted.
If you just put the sealer on the cover side, not on the engine side, you can usually take the cover off with the gasket remaining intact.
It can leak terribly, if that's what you're asking.