Keven
Don't get me wrong, I like SO2 powered fridges. They gurgle and spurt and make so many neat noises. If it wasn't for the fact that it smells horrible and can be corrosive as you mentioned it would be a fantastic refrigerant that would most likely still be in use since it is not a large greenhouse gas and isn't an ozone problem child. The compressors are nice and quiet because of the low head pressures too. Kind of like R12 vs. R134a, the old 12 units had less head pressure and therefore sounded much quieter. I think that you are on to something in saying that R12 could have been used for longer in sealed units since they rarely ever leak out compared to cars. I think that one forgotten CFC refrigerant that should have lasted longer was R114 which was exclusively used by Frigidaire. I've got two fridges that are equipped with it. They stopped using it by the 50s. When the fridge is under normal load in normal room temperature, the high side is right around 0 psi! Talk about low pressure! In fact, one of the units that I have that has this refrigerant started to leak oil around the electrical terminal of the meter miser rotary compressor. As Travis mentioned, Westinghouse had rubber seals for the terminals and Frigidaire, at least back then, was no different. The later meter misers switched to a much better metal glass seal. I was able to save the unit by stopping it in the nick of time and I only lost a little oil and barely any refrigerant. Try that on a modern system with high pressures even when the system is off! Because of the low, low pressures that R114 works at I was able to plug up the terminal with a special add on rubber seal kit and it hardly lost any oil or refrigerant. Normally after an episode like that you would loose everything and would have to fill it back up once it is plugged up. She purrs along just as quiet and efficient as ever, it only uses 110 watts for a 9 cubic foot fridge! People complain about the old fridges having these CFC refrigerants but they don't understand that they rarely leak out of a sealed system and when they do it is a tiny amount. Heck, you had to try to make this R114 leak out!
Fun fact, R114 is still used to this day in the Navy in their large centrifugal chillers. The reason? It works at about 0 psi on the high side as I mentioned so it rarely leaks out and if it is exposed to moisture it will rarely take in moisture laden air.