Can I rejunvenate a rubber o-ring?
O-Rings are (or should be) cheap - if they are not, try to establish exactly what size they are and shop around; you should be able to find them for a pretty low cost, and replacing them is the right approach, even for "one more year."

While you can try to get a little more life out of them by greasing them up with a pretty stiff silicone grease (typically found as o-ring grease or vacuum grease) that will likely cost more than new o-rings if you don't already have a tube (it helps improve life if applied sparingly to new o-rings.) Since you mention that the o-rings are cracked, I should mention that you may find that they break completely at the cracks when you are handling them to apply grease and re-install them. If everything smiles upon you, you might manage to pack enough grease into the cracks to stop your leaks - but replacing them really is the better approach to try.