Seeing these posts about going BACK to R12 are a little scary to me. This would require EXTREMELY thorough flushing and maybe a fresh compressor. the introduction of any R12 into an R134 is bad news and can cause some serious problems. These two compounds are to be kept completely away from each other. This is why they changed the fittings, and guage systems, so that you couldn't contaminate one with the other.
Just my thoughts,