Freon requires different types of oils than does R134a. Which system are you asking about? If its R134a than M.B. recommends only there own PAG oil. However since the older cars w/GM compressors require ISO 150 oil & Nippendenso compressors require ISO 46 oil one(1) weight of oil isn't correct. With R134a systems stay with PAG oil as most ester oils will break down under extreme conditions. Use "double end capped" oil, as it can be compatible with small amounts of oil from R12(freon) systems.
Can too much oil(or incorrect type) cause problems; Yes & that is the cause of most a/c compressor failures. Most shops don't have correct information on this subject(dealers incl).
MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH