I've tried several refrigerants over the years, and refrigerant substitutes. I've noticed that if it's an original R12 system, then R12 will work heads and tails better than anything else, period. The other options will be varying shades of "not as bad as R134". The only thing I've encountered that even comes close is a product called "Freeze 12" that gets pretty close. But R12 is still the cat's meow as far as I'm concerned.

I have had a couple W126's, both of them the previous owner had done the R134 conversion, and on both of them I went back to R12. There must have been a good 20F difference in vent temps both times, no exaggeration whatsoever.

I guess the main factor is, I live in Florida where summer is 2/3rds of the year and it's normally 98 degrees. I can't live with vent temps in the 50's, that would be miserable. With a properly functioning R12 system in my W126, the car could make itself uncomfortably cold inside, I'm talking ambients easily in the low 60F's, on a 100F day and at a dead stop. With 134, and with most of these "alternatives" you'll be lucky to see 50F vent temps.

The only one I would recommend would be Freeze12, but if you live in a hot climate just bite the bullet and pay the money and go back with R12.