Here's a breakdown of why:
* Engine Out (Likely): While *theoretically* possible with the engine in the car, access to the valve stems is significantly easier with the engine removed. This adds considerable complexity and time to the job.
* Head Removal: You'll need to remove the cylinder head(s) to access the valve stems. This involves removing numerous components, including the intake manifold, exhaust manifold, timing chain (or belt depending on the rebuild), and various other sensors and components. This is time-consuming and requires careful attention to detail to avoid damaging parts.
* Valve Spring Compressor: You'll need a valve spring compressor to compress the valve springs and allow you to remove and replace the seals. Using the wrong tool here can easily damage the valve springs or valves.
* Potential for Damage: There's always a risk of damaging valves, valve guides, or the head gasket during this process. If you're not careful, you could end up with a much bigger problem than just worn seals.
* Precision Work: Installing the new seals correctly is crucial. Improper installation can lead to oil leaks and further engine damage.
Since the engine was recently rebuilt (24k miles ago), the difficulty is somewhat mitigated. The engine should be easier to work on than one that's older and potentially more seized. However, you are still dealing with the complexities of removing the cylinder head.
The oil in the spark plug wells strongly suggests worn valve stem seals. This is a common cause of this problem.
Recommendation:
If you're not comfortable with engine work of this complexity, it's highly recommended to take it to a qualified mechanic specializing in older vehicles or Nissan/Datsun Z cars. The cost of doing it yourself, including potential mistakes, could easily exceed the cost of professional labor. The time investment alone will be significant. Weigh the cost of professional repair versus the potential cost of mistakes and your comfort level with the job.
