Thanks EV2, appreciate the offer.
Will let you know if I need it.

Thanks for all the detailed replies, learning a lot.

Another couple of questions based on above :

How can I tell what type of refrigerant was used to charge the restored system if there were no obvious changes to valves etc?

If 134a was used and can be replaced with R12, would a shop need a 134a machine to remove the 134a or can it be removed with any machine?

Would it need to be somehow "flushed out" of all previous contents before recharging with R12?