I wasn't sure if you stuck two leads into the liquid or the method you described.

So it's a simple conductivity test. I wonder how much the resistance changes with time and depletion of the corrosion inhibitor?

Enough to eat through your heater core and cause you big headaches....
LOL

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html