WmHarlow,

Maybe the 300D had the R4 earlier than the 240D. My wife had an '80 240D with a york. My daughter's '81 300D has an R4.

I prefer the york for it's simplicity and it's inexpensive rebuild. But the R4 probably takes a little less torque to run, a big advantage with a Benz diesel.

Have a great day,
Larry