Well, last summer, Steve already had me thinking hard against r134 conversions. I was at NAPA yesterday and asked their r12 price. It is 29.50 per can, and requires a 609, of course.
After I have been through converting some systems, I now wish I had left them R12. As a matter of fact, I am currently flushing the a/c in my old truck (78 Ford that I bought new,) to change BACK to r12. This is a unique case because it has a york compressor that will just not cut it at all with r134.
I am flushing EVERYTHING, replacing compressor and filter drier and charging with r12 and UV die. If a leak turns up, I don't want to be forced to waste r12 for a UV die charging. The dye will already be in there.
Changing back may be a no-no, but it's that, or change to a Sanden compressor system and spend $700 or so.
I shudder to think about converting a Benz back to R12, but I might end up doing it.
Wish me luck,