Seals, including oil seals, have undergone a great development in recent years and are totally unlike the original product. PTFE has taken over the oil seals market for modern engines mainly because traditional oil seals started causing more and more problems. Such as evaporation of chemical plasticisers from the elastomeric material, which eventually caused engine oil leakage. Now, the focus is more on durability and frequency of servicing.
Examples of defects
It is important for the spark plug to produce a strong and consistent spark in order for the combustion process to be efficient. Over time, the spark plug can become worn or dirty, which can affect its performance. This is why it is recommended to regularly inspect and replace spark plugs as needed to ensure optimal engine performance.
Use a flat paint scraper, or the smooth side of an old hacksaw blade, to remove very carefully all traces of carbon and old gasket from both faces.
ERIKS
The other way oil seals work is by stopping outboard materials that can damage the machine or contaminate its lubricant. The outboard materials that the oil seal will need to stop depend on the application. However, the most common kinds are dirt, moisture, and the particles produced during manufacturing.
Figure 4 shows the features of a JTEKT oil seal.

It is quite common for a groove to develop at the sealing lip at some point due to long-term use. As a result, the new oil seal no longer fits and seals properly. It is not strictly necessary to replace or repair the entire shaft. Take a closer look at the dimensions first. It may be possible to fit with a slightly narrower or wider oil seal next to the groove. Alternatively, using the Speedi-Sleeve repair kit, repair the running surface under the seal.