Service finds Oil in #4

Recent service found oil in my #4 Sparkplug hole. Due to the fact there is no oil retention ring, ie a O-ring to seal. The Toyota dealership looked for every possible option only to find no explanation besides an improper fitment or a bad cylinder head.
As they try to thumb through the delicate pages of the warranty to find a solution. I figured I ask here before i'm stuck in between a rock and hard place.
So has anyone heard or had this problem?
It's a 2002 Ext Cab Prerunner Six cyl. 92,000miles

 

I can understand them doing a compression check to see if the piston rings were worn and letting oil get by but I can't see how oil in the cylinder could be caused by a bad valve. A bad valve seal (most likely the intake valve seal) on the other hand could cause oil to leak down the stem of a valve and eventually into a cylinder, but a compression check can not detect a bad valve seal. A compression check would not spot a bad EGR valve either, and I cannot see how an EGR valve would cause oil to get in the cylinders since it strictly deals with the exhaust system. Now if there was oil in all of the cylinders, or a lot of oil in the intake manifold as well then I would say there could be an issue with the PCV system (maybe you meant PVC valve instead of EGR valve). Look for oil on the back of your throttle body or in the intake hose. If you see oil in there then you either need a new PVC valve (I'm not sure where they are located or how the system operates on this engine), or you will probably have low compression an a few cylinders which is causing blow-by and the blow-by is causing pressure to build up in your crankcase and forcing oil into the PVC system. If there is no oil in the intake manifold or tube then my bets would be valve seal if compression is good in #4 or bad rings if compression is low.

Does the truck smoke when you drive or accelerate? Does it smoke a bit when you first start it but then stop smoking after you drive for a bit?

 

Compression test for excessive carbon Your going to have to explain that one to me.

 

yes to much carbon will raise the compression but you are talking alot and the check engine light should have come on pointing to the problem causing the carbon build up. these engines almost run to hot and high compression to have carbon problems.

 

Yes, that will raise your compression ratio, but a compression test does not show compression ratios. It only shows that you cylinder has the ability to compress air.