Just some info about expected life of glow plugs, which may help someone. I have found ( at 85,000 mls 6 years,) that 3 out 4 glow plugs were not working, and have replaced them today. Symptoms were that engine refused to started when temperature below freezing, and a somewhat lumpy, smokey start when it did.
My recommendation would be to replace glow plugs at the same time as the timing belt (72k).