Just like any project on your W123, sometimes things don't go as planned. On this car, two of the glow plugs had been rounded off by a previous owner or mechanic.

They then gave up and left these old plugs in there. As expected, one of the two rounded off plugs was the bad one.

It just took patience and some vice-grips to convince these to come out. There was so much carbon build up the "squeaked" as they rubbed on it on the way out. Reaming them made the new plugs go in easily.