I have had much experience with this issue. You can only change over when: The compressor and the hoses are changed as new. I have seen the old hoses used and they are not barrier hoses. They will absorb some or all of the oil and the compressor will die. If you do not flush properly, you will have an acid corrosion problem (I don't know why, I'm not a chemist), but I have seen it before many times.
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM