Any proof out there for this? I haven't found any. The later cars had afterglow built in, so I'm skeptical that it wears them out significantly. I've had the same glow plugs for six years, roughly half of that with the purple wire disconnected and I have no complaints. I've seen people with a stock setup talk about replacing their glow plugs constantly, so I would be surprised if it mattered at all how long they glow. They live in a pretty harsh environment regardless.

Still, one anecdote doesn't constitute proof so I don't claim it as a fact.

-Rog