Good solid references :

sight glass specific non MB first one....

http://aircondition.com/knowledge_base/TheBasics/Components/ReceiverDrier.html

http://aircondition.com/tech/questions/30/

http://www.aircondition.com/tech/questions/19/What-are-the-Benifits-of-Leak-Testing-with-Nitrogen%3F

http://aircondition.com/knowledge_base/LeakDetection/OtherMethods.html

http://aircondition.com/knowledge_base/TheBasics/Flushing/BlackDeath.html

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

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

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

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