Most cars built before 1981 don't have hoses that can hold R134a. All rubber hoses should be replaced before retro-fitting with R134a. Most all replacement hoses have the inner "barrier" needed to withstand the pressure.
G.M. reccomends only ISO "150" pag oil for A6 & R4 compressors. Note M.B. sells only one weight oil & that is WRONG!! Nipp compressors need ISO 46 weight oil. Both of these are for R134a only. "Double end-capped" pag oil is the best.
[This message has been edited by M.B.DOC (edited 07-08-1999).]