I would just check it upon opening . . . if it seems good . . . . just use it. You may want to pour it out to see if it's separated, but I wouldn't do much more than that.

Half life of CARBON...
LOL
I think that is the half life of an isotope or something of carbon.... meaning the radiation is escaping at a certain rate.....not that the carbon itself has any half life..

I bought Brian's car at a bargain a while back due to oil use.... one of the main culprits was a beat up copper washer on the oil pan.... the other major user was keeping the oil near the max mark.. when I dropped it to half way between the marks it really made a difference... the other factor was a leaking valve cover gasket....

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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