Valve Stem Oil Seals
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Intake valve uses upper "O" ring seal. Exhaust valve uses upper "O" ring seal and lower umbrella seal, seated against cylinder head.