One of the worse thimgs you can do with A/C is to use too much oil. I would not switch from ester to PAG without flushing the system. The story about most conversions is that they worked (for better or worse) because the mineral oil just sat around in the system and didn't mix so one could forget about it for the oil calculation.
When the system has too much oil the oil impedes flow and causes a strain on what is a gas compressor. Too much liquid and its toast.
The problem is that both ester and PAG will flow with the 134 so you can't just add PAG. This is my speculation, I have read nothing on the subject.
We used ester successfully in the bulk of our conversions. I wouldn't change without doing it right. And if I was doing it right on my own car I would be changing it back to mineral oil and R12.
Bosch Master, ASE Master, L1
33 years MB technician