JHZR2,

I would not tempt fate and fix something that is not broken. If your present set of plugs work, and are not stuck, how have you improved the situation by replacing them with new ones? And if you go to replace them and one or more are stuck, and you damage them in the process, they won't work and you will have to replace them. When you are done, you will have at least temporarily "unstuck" glow plugs, but they will be no more functional then the ones you have in there now.

You apparently have an unusually robust set of glow plugs, or a set that is nearly perfectly matched to the glow plug relay, or are just lucky. I guess giving them a spritz of WD-40 or PB Blaster or Liquid Wrench every now and then to ward off the demons might not be bad, but I would definitely not replace them as preventative maintenance. There is documentation of problems getting them out, having poor quality plugs from any manufacturer as replacements, and generally difficulty reassembling, requiring reaming tools and the like. And, on your engine what makes you think a new plug is less likely to stick than an old one that may not be sticking yet?

I have changed glow plugs on our 240Ds and the 220D a number of times each, and never had a problem. Some were a little distorted when they came out, but I have never had one stick. The biggest problem is getting good access so you don't apply any bending moments as you try to remove the old plugs.

Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)