I considered changing the condenser on my '86 420SEL once; I learned there was a parallel-flow condenser for the Diesel 126-series right before the 126 was phased out: Mercedes-Benz genuine part, can't comment on if the fittings are in the same place, but they probably would be.
I admit I have not been able to get more than marginal performance from my car's refrigeration system in the 10 years I have owned it. It had been converted to R126 when I got it.
I think I will have to remove the dash and start from scratch. Perhaps the evaporator is dirty; the air flow seems fine, but it would only get cool, like air outlet temps of 65-68 degrees, at best. I did not buy the condenser because when I turned a water hose on the condenser, it made little to no difference, so I wondered if that was the problem with mine anyway.

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Providing a home for these cars:
1951 Buick Special De Luxe
1977 Rolls-Royce Silver Wraith II
1970 Rolls-Royce Silver Shadow
1986 Mercedes-Benz 420 SEL
2005 Mercedes-Benz E 320 CDI
2012 GMC Sierra 1500 4X4
1927 Pierce-Arrow Series 80
1931 Pierce-Arrow Series 43
1926 Ford Model T coupe