Why are you using the term ' R12' and Freeze 12 like they are the same thing ?
Freeze 12 is part 134a...
Do you really know which you have ?
I suspect you are about to mess up your system and it cost you a lot of money... because you are not listening...

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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