Oil and engine wear
In my experience, as long as the oil and filter are changed every 3000 miles or three months, I have seen no real difference from one oil to the other. As has been mentioned throughout this post, frequency, I think, is the key.
My 103 has 127000 miles and is rapping at start up and consuming a lot of oil (1 quart every 400-500 miles).
I am planning a head job in the spring. I'll pull the head and send out for machining and valve job. Based on all the threads I've read, valve seals are probable culprit. Will do valve job to be sure.
As a side note, I think it's a little odd that this type of work (vavle job) is accepted as "routine maintenance" on these cars. My expectations prior to buying this, my first Mercedes, were that a Mercedes was bullet proof and long lasting. My car has definately not lived up to my expectations.
Have a great Holiday,