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).