I would not put Freeze 12 into a car that I was about to sell. It will make it impossible for the future owner to get professional AC service on the car. There are not shops that will recover the stuff. I suspect that most of it gets dumped into the atmosphere by owners as it is and never reclaimed.

Freeze-12 is mostly 134a, but contains other refrigerants to help carry the mineral oil. That's why you can run it with the old oil in the system - until those other refrigerants leak out! Then you have no oil migration and your compressor fails as a result.

Stay away from this junk. One more thing, did you add oil with the refrigerant twice? Before you did that, did your remove the old oil? If the answers are yes and no, you almost certainly have too much oil in that system.