DIAGNOSIS Yeah, this one's common. The silicone sealing gasket absorbs oils and residues over time, getting tacky. It's not supposed to feel like that.
FIX Remove the gasket from its groove in the lid. Wash it in warm, soapy water—dish soap is fine. To deep clean it, you can soak it in a solution of one part white household vinegar to three parts warm water for 15-20 minutes, then rinse thoroughly. Let it air dry completely before putting it back. That should cut the grease and restore the surface.
IF THAT DIDN'T WORK If it's still sticky or has become stiff, cracked, or misshapen, it's done. It's a wear item. Order a new Presto replacement sealing ring (the part that fits the 16-quart aluminum canner). Don't try to use the canner with a compromised gasket; it won't seal properly.
HEADS UP Never use bleach or harsh chemical cleaners on the gasket. It can degrade the silicone. Also, never store the lid with the gasket compressed in place for long periods. Store it separately or at least unlocked to prolong its life.