My limited experience as a diesel owner means this info. is from my mechanic......
Never change glow plugs unless you have cold starting problems. They either burn the ends off, which means they will come out easily and safely....
OR... they get misshapened on their ends with a ball shaped, hard crud that will usually get knocked off when removing the glow plugs and end up like a loose marble inside your motor.....lol...jem
The Silver Buffalo
Saturn with Blue OX towbar
WBCCI # 14067