Yeah, people don't realize just how little it takes to destroy a plug. Just the other day I was helping somebody set their engine. They had been running it a bit lean. Anyway, their engine was giving signs that the glow plug was bad, so I told them to take out the plug. He thought I was nuts because he had just replaced it a few flights ago. He took it out anyway, and lo and behold the plug had a frosty white appearance (bad plug).