R406A is supposed to be the only blend that will work with R-12 and mineral oil.
The whole problem is that 134A only mixes with PAG or Ester oils and these oils do not like Chlorides.
Here is a link to a company that sales the stuff but I list it only for the tech info.
What happens when one uses a Chlorinated Refrigerant (i.e. CFC or HCFC) in PAG oil made for R-134a systems?
PAG OIL (Polyalkylene Glycol) Refrigerant oil made for HFC (e.g. R-134a) systems CANNOT tolerate even minute amounts of chlorides, such as from aluminum chloride "coatings" inside pipes that formed from the original R-12 charge or having over .5% or more of "chlorinated refrigerants" in the system. Chlorinated refrigerants include the CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). R-11 (flush) and R-12 are CFCs. R-11 is extremely damaging to PAG oils, more so than R12. This information dates back to 1990-1991.
HCFCs include R-22, R-124, R-142b (blend components used in R-406A/Autofrost, Frigc FR-12, Freeze12, Freezone RB276, R-414A (GHG-X4), and R-414B (ICOR HOTSHOT).
Use of any of the above refrigerants or blend components in a system with PAG oil will mostly likely destroy the oil. There have been some attempts to make PAG oils to withstand chlorides, most notably the "Daphne" brand. The test sheet I saw still showed slight darkening of the PAG oil (Daphne brand) when mixed with R-12. Other brands of PAG oils turned black. When one services a car, one usually does not know if it contains Daphne PAG or not.
Not all CFCs/HCFCs are the same reactivity in destroying PAG oil. R-11 (the old "flush") is the most reactive by far, and R-124 is one of the least. Actual break down times will be related to ambient temperature and operating temperature as well.
A 16fl oz bottle of GM Delco "Refrigerant Oil R134a Systems" (other numbers on bottle: 1#12356151 Gr. 8.8 1#15-11
was purchased at a local auto parts store. The label also had the information "Contains: Polyalkylene glycol-New Jersey Trade Secret, Registry number 027586004-8550P).
A newly developed PAG oil, called "Daphne" or "Double end capped" PAG oil has been shown to be able to withstand chlorinated refrigerants, even R-12, MUCH better than conventional PAG oils.