Some of your statements make me think this site would be helpful also...

http://www.epatest.com/manual609.html

There are no 'drop-in' substitute refrigerants for any equipment category. This means that some changes in a system's equipment or materials of construction are always necessary when converting to a replacement refrigerant. The existing refrigerant cannot simply be removed from a system and replaced with another refrigerant. Usually the changes amount to replacement of incompatible seals and changes in lubricant. Filter-driers, compressors, and seals that are compatible with CFCs, HCFCs, HFCs and their oils are currently being developed; however, the replacements are not without problems. The new (POE), synthetic oils being used with HFC refrigerants are incompatible with as little as 1% residual oil, (PAG or traditional mineral), in the system.

NOTE:
HFC-134a still carries some concern about compatible lubricants. Lubricants typically used with CFC-12 do not mix with HFC-134a. Polyalkylene glycols (PAGs) mix properly with 134a at low temperatures but have upper-temperature problems, as well as incompatibility with aluminum bearings and polyester hermetic motor insulation. Ester-based synthetic, (POE), lubricants for HFC-134a resolve these problems but are incompatible with existing PAG or mineral oils.