older gasses are blamed for damage to the ozone layer so are no longer produced
add to the mix that you have a gas leak somewhere and unless it is found then any gas you charge it with will be lost
if you want to be certain about the gas advice look on the rating plate and all fridge gasses as far as I know are R something. R12 is a very early gas that did deplete the ozone layer. you can then research the gas type or post it back here and I am sure one of the refrigeration experts will tell you
but there is still a possible leak
Dave