glow plug related smoke at startup

[noMoreGasoline]

I have an '82 300D that i'd like to make a little less polluting.

After reading a few threads here, I know that the glow plug system is the reason for my excess smoke and poor idle on a cold startup. I tested this assumption today by letting the plugs heat up until the safety interrupt kicked in (about 20 seconds). Then I engaged the starter and what a difference! Much less smoke and a smoother idle... still not perfect, but better.

So as per one of the threads (and the MB manual procedure 15-710), i tested the resistance of the plugs. Zero on all of them. The manual says they should be less than 1000 ohms, but zero?? Does that sound right? I have no idea how old they are or what brand... but should i just replace them all?