I have always heard not to do the yorks with 134. Don't know the science behind it. I can say that all MBs with york compressors had hard time keeping the belts tight enough to pull the compressor at R12 pressures. I used to change out any that would to a Sanden or Diesel Kiki if only for the lack of belt problems and noise.
Bosch Master, ASE Master, L1
33 years MB technician