Looks like #5 is telling you something.

If the 602 is anything like the 603 turbo, you have to pull the intake manifold to replace the glow plugs. Consider the effort involved and the number of brittle injector line retainers that will break before deciding to replace only one glow plug.

Sixto
95 S420
87 300SDL
83 300SD ... $1100, see cars forum