R4 or A6?
 

I am sure this question must be answered in here somewhere but I can't find it.
How do I know if I have an R4 or A6 air con compressor?
The parts label is blank, because of my repeated engine compartment cleaning.
I have an 1984 300D Turbo
Compressor is making nasty noises and making the car vibrate. I don't want to give up on the R12 but I can't get it anymore and I obviously need a new compressor.
Thanks

R4

Thank you