I couldn't find the vac. line at the manifold, so decided to pull plugs instead. #6 looks fine, dry and normal. Also compared with a few others and firing end looks consistant.
Luckily or unluckely, I had my water pump replaced recently and I knew the color of antifreeze should be good and I do not see any signs of oil in the overflow tank.

Next seems to be getting under and look for signs of oil.

Any particular areas to start ? Any known weak O rings?