Here's why and what needs fixing:
* Valve Stem Seals: These small rubber seals sit on the valve stems, preventing oil from seeping past the valve guides into the combustion chamber. As they wear out (due to age, heat, or mileage), they lose their elasticity and allow oil to leak. Because the spark plug tubes are directly above the valves, the oil will collect there. This is the most common cause.
* Worn Valve Guides: Less common, but if the valve guides themselves are worn, excessively sloppy valve movement could allow oil past, leading to leakage into the tubes, even with good seals.
* Cracked Valve Cover: While less likely to directly fill the spark plug tubes, a cracked valve cover gasket could allow oil to escape and potentially find its way into the tubes. This would be more of a general oil leak than a direct filling of the tubes, though.
What you need to fix it:
This is not a DIY job for a novice. It requires significant mechanical skill and specialized tools. You'll likely need:
* Valve Cover Gasket: Replace this regardless, as you'll have to remove the valve cover to access the valves.
* Valve Stem Seals: These are the most likely culprit and must be replaced.
* Possibly Valve Guides: If the guides are severely worn, they'll need replacing too. This is a much more involved repair.
* Tools: You'll need a complete set of metric sockets, wrenches, valve spring compressor, valve seal installer, and possibly valve guide removal/installation tools (depending on the guide condition).
* Shop Manual: A factory service manual (Haynes or Chilton manuals are also helpful but less detailed) is absolutely crucial. It will provide step-by-step instructions and torque specifications.
* Mechanic's Experience (Recommended): Unless you have substantial engine rebuilding experience, this is best left to a qualified mechanic. Improperly installed valve seals or guides can cause engine damage.
Before starting any work:
* Verify the Leak: Double-check that it's actually oil and not something else (like coolant).
* Diagnose thoroughly: Consider getting a compression test to determine if worn valve seals are the primary cause. Low compression in one or more cylinders can confirm this suspicion.
In short, leaking oil into the spark plug tubes is a sign of significant wear within the valve train. It's best addressed by a professional mechanic to prevent further engine damage. The cost of repair will depend on the extent of the damage (valve seals only, or seals and guides).
