IMHO, the only proper way to convert a W124 from R12 to R134a is to change out the condenser to the R134a specific one, *and* change from a single aux. fan, to the double fan used in the R134a ones, as well as dryer/receiver and expansion valve. Also use only PAG oil.

We did the above to our 1988 wagon, and get's plenty cool for trips to Las Vegas.

:-) neil