Does anybody have a guess as to the most likely place for refrigerant leakage in a C4 B7 model? Dye hasn't helped, at least so far. I am hoping for obvious reasons it isn't the evaporator.
2012 is probably a bit early for 1234yf. You can tell from the filling/test valve ports. They are the first place to look for a leak and there are tools to allow replacing the valves with the system fully charged. Otherwise, likely evaporator corrosion if you can't see any dye around the rest of the circuit or an oil spot on the condenser.