Situation: During the site handover, the Ops team submitted a service request about a leaking air vent valve on one of the fuel coarse filters. My technician immediately said it was a faulty valve that had been like that during installation and proposed to replace it which costed us 700 Euro. But I'd seen poor work quality and lack of supervision on other systems during that time, so I was pretty confident the problem wasn't the valve itself—it was how it had been installed and put into service. I just needed to prove it. Task: I wanted to demonstrate that it was an installation issue, not a bad valve, by putting it back into service and observing exactly where the leak was coming from. Action: I asked Ops put it back in service and watched closely. Sure enough, the leak was coming from the bottom of the valve - at threaded connection to the tubing. I brought my technician over and we removed it. I reinstalled the valve using Loctite thread sealant. He was skeptical, saying it wouldn't work with diesel fuel same as last time and that we needed PTFE tape instead. I explained that the manual specifically said to wait 24 hours for the sealant to fully cure, which was never done last time, and I was confident it would hold. He wasn't convinced until the very end. Result: After 24 hours, we asked Ops to pressurize it again, and there were zero leaks. It proved my judgment was right—the valve was fine; it was just a bad installation. This was a great teaching moment for my technician. Instead of jumping to assumptions he learned to dig into the details, check the specs, and test your hypothesis properly.