My BMW is converted to 134. When the job is done right, one cannot really tell. Mine was done with new compressor (which is really the only reason to open the system and think about it), and meanwhile the expansion valve was changed too. The system works and is tight.

My hesitation for w123s is the R4 compressor... my BMW uses a nippondenso, IIRC.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)