A PA28 Instructor Pilot discovers an oil leak during preflight and has Maintenance take a look. Maintenance believes the leak is acceptably small; but when new students are brought over to view the leak for teaching purposes one of them detects a fuel leak in the same area.

Narrative

While my student and I were doing the pre-flight walk around of the aircraft to be flown I noticed evidence of a possible oil leak on the exterior of the cowling and looked inside to investigate. It did not take long to find that there was an oil leak. I went to get a member of the Maintenance staff to look and confirm the leak. Two tech's came out and they confirmed my suspicion of an oil leak but advised that it was minor and as long as there adequate oil for normal operations that the leak was not great enough to hinder the flight; so we continued the pre-flight. I noticed a fellow instructor was showing some new students how to properly pre-flight and aircraft before a flight. I wanted to share the experience with these new pilots so they knew what to look for should they ever come across an oil leak in their flying career. Their instructor said it was ok; so I took them over to the airplane and started pointing out the signs noticed prior to opening the cowling; and then continued inside to the engine and pointed out the oil leak. One of the students then pointed at cylinder #3 and said 'what is that blue stuff'. A fuel leak on cylinder #3 had been missed by an instructor; an experienced student; and two members of the Maintenance staff because we were too busy looking for the oil leak instead of seeing the entire engine.