The process of transforming from the liquid or solid status directly into the vapor phase is called sublimation. And that happens when a small amount of the hydraulic fluid vaporizes through the upper seal at a high operating temperature,
Once it encounters the colder external air, a thin film is formed by condensation at the outside of the shock absorber. In addition, the two forms are completely normal and necessary for the shock absorber. The vaporized fluid through the seal area will lubricate and prolong the service life.
The shock absorber is equipped with an oil seal, and it will allow a vaporized film to appear on the shock body, which is acceptable and fine.
When it comes to the actual leaking of the shock absorber, it will be easy to spot these fluid traces in the upper seal area.
The picture below shows the left one is normal, and the right one is leaking.
