Ok, so I finally figured out that apparently the VIN switchover reflects the change from ABS only to ETS/ASR and hence why the MC was changed however what the change was to the MC I don't know since the continued to look the same. Something internal must be different, and part numbers apparently aren't stamped on the MC so checking the unit isn't possible.

The crux of the situation is that I acquired a MC for the 92 300SD at a PNP and it came from a 95 S320 post vin switcharoo to ETS/ASR so according to MB it won't work, it's not interchangable. The brake pedal on the 300SD travels a lot even after fluid flush so I was thinking it was probably not going to last.

Funny thing is that the reservoir mounted on the new MC has a part number that doesn't come up in EPC as having been used on the S320 and I can't find information for the reservoir fitment although the number does come up on parts dot com as a 'reservoir' but without model association.

Anyway, the problem is solved, MC difference has been determined.

steve a

__________________
Steve A
92 W140 OM603
97 VW Jetta TDI
90 Passat variant TDI 6 speed MT
94 Chevy K1500 6.5TD
05 E320 CDI
+ others