During a routine maintenance service, what should you do next if the transmission fluid is a dark red color and the rear seal is leaking?

The reasoning behind selecting the course of action involving changing the fluid and filter while advising the customer to replace the rear seal and bushing stems from the diagnostic clues presented by the transmission's condition. A dark red color to the transmission fluid typically indicates that the fluid is old, degraded, or possibly contaminated. This is a clear sign that the fluid should be changed as part of routine maintenance to help ensure the smooth operation of the transmission and prolong its lifespan.

Additionally, the presence of a leaking rear seal is indicative of a potential issue in the transmission system that needs addressing. Advising the customer to replace the rear seal and bushing not only resolves the leak but also prevents further complications that could arise if the leak worsens, possibly leading to low fluid levels and severe transmission damage.

By performing these actions—changing the fluid, replacing the filter, and addressing the seal issue—the mechanic is ensuring that both the immediate symptom of dark fluid and the more significant mechanical concern of the leak are addressed in a comprehensive manner. This preventative approach helps maintain the overall health of the transmission while being transparent with the customer about the required maintenance and repairs.