This one isn't me, I swear. I'm posting this for a friend. Really.
I have this wanna-be mechanic friend (female, if that makes a difference
) who decided to check the engine oil in the 914 she had recently purchased, and she put the oil cap on top of the air filter (both of which are black). She got called away, and when she returned to her car, she neglected to replace the cap. She drove off in the car and thought nothing of it. Later, when she discovered that the cap had gone missing, she searched fruitlessly for that oil cap in the engine bay. Needing to cover the hole left by the missing cap, she substituted a rubber gasket in place of the oil cap and went on with life. The following day, while on her way to meet an old friend for lunch, the car started making hideous noises and ground to a halt. It turned out that the missing oil cap had lodged in the fan of the aircooled engine, shearing off the clutch on one end and the fan housing on the other. The fuel injected 2.0 engine was now an expensive pile of scrap metal. For want of a nail, the shoe was lost, etc. She ended up buying another engine core, since the case in the 914 engine had a crack that had been sealed with JB Weld, and a mutual friend rebuilt the engine for her.
I think that a PPI would have uncovered the crack in the engine case, as well as the fact that the pristine looking body looked more like Swiss cheese underneath, but that's another story. And I learned from that experience and had a body man check out the 911 I ended up buying (from the same mutual friend).