I think we can conclude you need to clean the area around the front of your engine... really clean on that area with markings... then take some white paint with your finger and mash it into the markings... wipe off the top surface to leave it in the markings.... it should have BTDC and ATDC marked there... (?)

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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