My mom bought an early 2000's Jetta secondhand. It has the naturally aspirated 2.0, which I personally believe is one of the best 4-bangers on the market in that range of displacement. It had been maintained beautifully. Full service records, everything worked, even still had the stick-on plastic protectors on all the shiny bits of the interior. It worked perfectly for 2 years, at which point it started to behave in a way that I can only describe as demonically possessed.
The entire electrical system has seemingly developed a mind of it's own, and systems that share not so much as a scrap of common wiring will interact totally at random. For example (my favorite), if you turn the windshield wiper on the low of high setting, past the intermittent setting, it cracks the sunroof (always ideal in the rain). The blinkers don't work or work intermittently, but the emergency flashers work just fine... as long as the radio is on. It also likes to lock (or unlock) itself totally at random, sometimes after sitting for days. I've been through half of it with a good multimeter, and Mom took it to the dude who is supposed to be like THE VW guy, and neither of us could find anything wrong with it. Conclusion: Gremlins.
My 94 bronco, on the other hand, just keeps on ticking.
1967 Galaxie XL, Q-code, 428"
2012 Focus SE (appropriated by the Mrs.)
1994 Bronco, 5.0L (called back into service from its well-deserved retirement)