What should be inspected on the hub oil seals or axle seals?

When inspecting hub oil seals or axle seals, the primary concern is to check for signs of leaking. Leaks indicate that the seals may be compromised, which can lead to a loss of lubrication and potentially result in significant mechanical failure or damage to the vehicle. If oil leaks from the seals, it could mean that the seals are worn or damaged, posing a risk to the axle and wheel assembly.

Other options like the presence of rust, color of the seals, or diameter of the seals are secondary concerns. Rust can indicate corrosion elsewhere, but it does not directly affect the function of the seals themselves. The color of the seals might help in identifying the type of material or if they are deteriorating, but it is not a direct indicator of their operational integrity. Similarly, while the diameter of seals might be relevant for installation purposes, it does not inform you about their current condition or ability to perform their sealing function properly. Thus, the most critical aspect to assess during a pre-trip inspection is the presence of any leaks, ensuring that the vehicle maintains proper lubrication and safe operation.