Final answer:
The correct option is a) the U-joint has been properly lubricated. Fresh grease at all four trunnion seals after lubricating a U-joint usually signifies proper lubrication, not worn components, and no further action is required unless there is visible wear or damage.
Step-by-step explanation:
When lubricating a U-joint, if fresh grease appears at all four trunnion seals, the U-joint has been properly lubricated. This is an indication that enough grease has been pumped into the U-joint to reach all the seals and exit them, which means that the bearings inside the U-joint have been sufficiently lubricated. This does not necessarily indicate that the bearings, seals, or trunnions are worn. It is a normal and expected outcome after a proper lubrication process. However, the actual condition of the U-joint would still need to be visually inspected for wear or damage.
The trunnion seals are designed to prevent the leakage of the grease. If fresh grease is visible at all four seals, it suggests that the lubrication process was successful and the grease is able to reach all parts of the U-joint.
Replacing the bearings (option b) or the seals (option c) may not be necessary if the U-joint is functioning properly and the grease is reaching the necessary areas. Similarly, if the trunnions (option d) were worn, there would be signs of grease leakage at those points.