I just came from the climate man because my compressor was changed and I needed a new filling. Actually, I have an R12 system, so only the substitute R413 works.
All tinneff and money tailoring, says the man, is decisive only the oil in the system, filled in oil and R134a refrigerant, 60 EUR and was finished the conversion

He explained this to me: The old oil in the R12 plants is not compatible with the new refrigerant R134a. It is flaky (!?) and thus no longer transported in the system, ergo: gaskets are brittle or even the compressor runs tight. The old oil is still in it, so it will continue to be flaky, but now the new oil is still there, it will be transported and lubricates all the important parts of the plant.
Have you heard of this before?
So I'm going to do the guinea pig and report it.

@Rainer: puts a compressor to the side

Welcome
Jörg