Volvo 8-valve overhead cam redblock engines (B21, B23, B230) have four valve guide seals, one on each intake valve. None are used on the exhaust valves, since the exhaust gasses will push out any oil that slips by. The intake valves need seals though – without seals, oil would be sucked/forced into the combustion chamber.
Want to replace them? Read the rest of this article on Valve Guide Seal Replacement.