It is illegal to manufacture R-12 in the US, it is not illegal to sell existing stocks. My wife is licensed and she could go buy some R-12 today. It is still completely legal
in some other countries. You're not in the US exactly, I have no idea about PR laws, but you may benefit by sailing to the next country where R-12 is more readily available.
R-12 is an excellent refrigerant, 33% more efficient than R134 IIRC, so converting to R134 or one of the hybrid R-12 replacements
will make your compressor
run a lot more. No big deal on a car or in a house, but a really big deal on a boat where you have to make your own electricity. Additionally, R-134 tends to leak out of conventional O rings and seals
so they need to be changed as well. I think they need to be Viton, not rubber.
You would be best off finding a place to evacuate, test, and refill your existing system with R-12. They can solder on proper fill ports
if necessary, refrigeration
guys do it all the time. They even have self-piercing screw on fittings that require no soldering. If it can be fixed than all is well and simple.
If it can't be fixed cheaply I would have to recommend replacing the system with one designed for R134 so that it won't suck your batteries dry in a half a day.