I agree that the glow plugs should be removed and checked every year or two to prevent problems, reinstall with anti-seize and clean the intake while its off, check the injector lines, fuel lines and return lines...these are all good things.
Also I suggest tackle the job when the engine is HOT, as soon as you shut it down remove the intake manfold and get right on them...parts always come apart easier when hot and when mine were done on a hot engine all 6 came out without a hitch.
AFAIK they were the originals in there for 7 1/2 years.