Have it converted to R134a but charge it with one of the HC12 replacements. They are more efficient than R12 or R134a, take less material to charge the system, and cost less. They are also more environmentally friendly, and do not require a change of the oil type. It is compatible with either.

My favorite brand is EnviroSafe, as they have a product that will seal small leaks in the metal parts of the system. I've charged two leaking sytems with it and have been very satified. Both now cool well and don't leak.