Weird stuff happens, any theories?

[jonmc56]

Friday night we took our truck to the local Dairy Queen cruise in. I normally don't open the hood at these kinds of things, but somebody asked me a question about the engine, and I left the hood open after that.

At the end of the evening I started the truck to leave, and it was running really rough. It died a couple of times when I put it in gear, which isn't normal. When I got to the stop sign at the parking lot exit, I noticed that I had no power brakes. Something was up, so I pulled over and popped the hood. I saw that the cover to the brake booster check valve was missing (see pic), and then found it sitting on the battery.

I limped the truck back to a store to get some super glue, and once I glued the cover back onto the check valve, all was well.

What the heck? Any theories on how this happens? I know one possibility is that someone messed with it, but that seems like a stretch. Maybe it fell off, then the air from the fan blew it around the engine compartment and it landed on the battery when I shut the engine off? Other ideas?

In any case, not impressed with the quality of this check valve...