I have a considerable amount of smoke at startup and a little bit just driving around with the car fully warmed up. This is on a '74 240D.
NHDOC replaced the valve stem seals in his '75(ish) 240D and in this thread, he said it didn't reduce his oil consumption much:
Valve Stem Seal Question
Hopefully your results are different. I'd like to do this on my w115 as well, so I'll be waiting to see how you make out. Thanks for letting us know!