You should use r 12 replacement gas, there are serveral types available and are more exspensive the R134A but not much ,the difference in the r12 replacements is some have dyes in so you can trace any leaks but the all do the same job , i wouldn't advise using r12, some say r12 its legal ,but if your caught releasing r12 (r12 is a cfc) its a£20000 fine max so i would call that illegal lol to retro fit a r134A system is expensive because most of the components have to be change as the molicules of r134a are much smaller andwill seep out of rubber pipes and seal design for R12 but if you need to regas every year thats a good sign you need new seals anyway, best thing is take it to a specialist in aircon not some monkey down your local garage they will advise you better than 1000"s opinions on the internet, many thanks John.... [Non-text portions of this message have been removed]