Bad glow plug(s)

[chronometers]

I am getting the glow light on the dash after starting car and then it goes out. My understanding is that this indicates one of more glow plugs is bad?

I pulled the glow plug harness from the relay and tested each port with OHM meter.

Plugs #1-5 registered 1 OHM.

Port #6 registered nothing. There is no continuity.

I confirmed the glow plug relay was putting out 12V at each of the pins and it makes a clicking sound.

Does this mean this #6 is a bad glow plug? If so, should I change the others at same time? I've read about the horror stories of replacing these plugs and am going to have a mercedes tech with experience do it.