2000 Pontiac Gran Prix engine leak

2000 Pontiac Gran Prix mileage: 100,000. Severe engine leak is probably from the distributor housing. I have been told that the plenum, intake manifold and one head must be removed to extract the shaft and replace an O-ring which is the cause of the leak. Rather than taking the shaft out, why couldn't you seal the top with silicone for example and reduce the overall effort? Is there any downside, since the internal o-ring would still leak?