Has anybody done this retrofit on their 735il. I have a 90 735il. It's not getting as cold as usual. I stopped by a shop that says they can order either of two retrofit kits. One allows the addition of an oil to my R12 and then add the R134a. The other requires a vacuum of the system and start with R134a from scratch. I've heard that R134a doesn't cool as good. Is that because of the method of conversion? Has anybody been successful and feels that they recommend a certain kit? Any help appreciated. Thanks in advance