THis from another thread:
If you plan on retrofitting to R-134a you should replace all the O-rings, install new charge fittings, a new dryer, bring it to an A/C shop to have them check your work and get the system flushed and charged. GL
On this forum or a parent forum (maybe lumina APV), there have been a few threads about refrigerant R143a....yes 143, not 134, that can be used as a direct replacement for R12. I do not know about its availability but I think remembering that was from a member living in EUrope. MAy be verify this option.....
ALso, a rerigerant sold as "RED TEK refrigerant" is available in Canada and sold as a direct replacement for R-12 at Canadian Tire.
EDIT: ahh....verify this
http://www.redtek.com/win_12a_faq.html
http://www.canadiantire.ca/AST%2Fbro...bmLocale=fr_CA