i took my car to a AC shop, they filled my system with liquid nitrogen to check for leaks. My leak is either very small, or the bozo that filled it last year didnt fill it enough and the R134a ran out within 6 months.
as for your R12 compressor, Most AC shops have fabricated adaptors so that you can fill r12 system with R134a. i dont know about where u live, but R134a is good enough for me.