Stephanie,
I assume you mean the O-ring for the lid. It only take a very tiny leak to let air in and it won't prime. If it's chewed up, replace it. Have you tried silicone lube on it? Being chewed up you may need to glop it on thick to get a good seal to run it temporarily until you replace it. If you need to get it running right now, which it sounds like you do, and don't have silicone lube, use vaseline. This is only temporary and not good for the O-ring as vaseline or any petroleum product will eventually turn it into a gooey blob. After this, when you do replace it be sure to clean all the vaseline or whatever off the seats. Pool stores have the silicone stuff and it's always good to keep a tube around.
Al
BTW: Welcome to the forum.