Not sure this counts really, as it was damage (rust) that presented itself in an odd way.
Anyway, I was travelling down the A45 one winters night in my wife's austin 1100. It was well rusted, and past it's sell by date really. Suddenly, the offside headlight pops up and backwards, blinding me in the process. With it flapping about, it was like looking straight into a strobe light from 4 feet away...!! Luckily I was in the nearside lane, and knew there was a turn into the slip-road down to the Peugeot garage ahead, so managed to get off the main road OK. Stopped and manoevred it back into it's rightful place, and gaffa taped it back on. Oddly, the gaffa tape help firmly on the rust for many months..!!
Eventually replaced the car, and while I was showing the *new model to my neighbour, there was a grumbling sound, and the whole rear end fell through on the subframe of the old girl. (I'd driven it back from work the same afternoon
) It just gave in after seeing herself replaced by a younger model I suspect, so went to the scrappy the next morning
* it was 3 years newer (so still old) Morris 1100 I bought for £25. Did me for 2 years without a problem and sold it for £35. (having taken the radio out and sold it separately for £5...)