It is illegal to use R12 refrigerant, and has been since around 1993.
You also now have to be F Gas registered to work with refrigerants.
All registered Engineers and companies can be found on the REFCOM website.
Suggest you get an Engineer to leak test system first, if leak can be repaired a drop in refrigerant can be used in old R12 units,with the R12 being properly recovered for destruction.
Besides you need more than just a connector to charge a system correctly.
Big Tone the fridge man, September 2009