What is the best type of oil to use?

[otter74]

With high zinc oil, factor in taking your plugs out every other month to clean them because zinc buildup will cause electrical continuity that degrades the spark. Don’t believe me? Check them with a multimeter.

Huh. I've used 20W50 VR1 in my 911 for a decade and have never had to touch the plugs other than changing them once.