The price of R12 has dropped dramatically because of decreased demand. R12 will probably be around for a long time. Only downside as mentioned above is that you need a license to buy it. If I were you and the '94 still has R12 (but I suspect it may be 134A), I would keep it that way. Evaporator failure is a known problem no matter which type of refrigerant. The rest of the system seems reliable but like anything else, as it ages, it will need service. My '90 300E had the evaporator replaced 4 years ago. The receiver/dryer and expansion valve were replaced (as well as vacuum motors) and the system was pumped down to check for leaks - none! Original compressor and 4 years later still cools better on 95 degree days than anything newer I have.