Agreed the 124, R12 systems are not the best performing systems ever made, but when working right, they work well. The fault with them lies in the failure rate of components, not the lack of cooling capacity when using the refrigerant that they were designed for.

The problem when converting is that they are designed on the edge, so there is no performance margin to be used up in the conversion.

As far as converting back, if you will flush everything, replace filter drier, put in the correct amount of mineral oil, you can have a decent performing a/c system. My 124 is still R12 and performs well. Keep in mind that I live in Texas and deal with some pretty hot days, and I still stay very comfortable.

Have a great day,