Some of the shops have machines that flush the entire system, but I know nothing about them or their use.
Typically flushing is done by disconnecting everything and flushing each hose and component individually, then ensuring that the flush is completely blown out of each piece. Then the compressor is removed and as much refrigerant as possible is poured out, then the correct amount of Ester oil is poured in the compressor and reinstalled. Once the system is reassembled, you turn the compressor several turns by hand to see that it is not liquid bound at startup.
Given all this falderol, you would be better served to simply repair your leak and recharge with R12. This, in most cases, is cheaper and the result will be an a/c with maximum cooling capacity.
Have a great day,