If you are going to use R12 I wouldn't worry about changing the compressor to a Sanden. If you do anything add a second condenser. vstech is currently exploring a kit for 123s and the original poster in the dual condenser thread has successfully added two PFCs.

If your system is currently working and on R12, I'd leave it alone. Is it underperforming? Why do you feel you need to do anything? What are the pressures and temperatures? You may spend a lot of money for little improvement. Most that do all the changes do so because they are running a refrigerant other than R12 and are trying to bring the performance of those refrigerants up to R12s level.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD