With factory parts, some oil will appear on the plug and be visable in the bottom of the tube since it is under the oil level in the casting.
The engine will smoke for a couple of minutes as well after start up /plug change.
There is a couple of people that make a fix for the problem , which is basically a sleeve that fits in the casting and seals to the OD of the tube..
I am running Autolite plugs and leave the compression rings on.