Best thing you can do for the 80s models with the 616/617 engine is the Sanden upgrade and continue to run R12 as long as you can find it.

Don't make the mistake I did and wheeze along with a replacement R4. It is a crappy design and no amount of modern technology can cure that case of ugly.

The later 80s 126s and 124s have Denso compressors which are good.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech