Excuses in this category must invoke a feeling of sympathy, great importance, or unbridled imagination. Since most horseshoers can't afford a decent watch anyway, the concept will seem trivial. Instead, tell them you got stuck behind a presidential motorcade, and the CIA jammed your digital clock. But never say the transmission. Anyone who has ever blown a transmission knows it takes fourteen days to fix one right.
Nobody likes balljoints, anyway.
Kidnapped by aliens. This always sounds important and even though there isn't a vet within 42 square miles that will even talk to you, it nonetheless is quite effective. Make sure you pick one that has been dead for at least ten years. It is horribly embarrassing if the mystery vet drives up while you are still going over the excuse. Explain to your client how a simple root canal turned into something worthy of a paper in a medical journal.