I'm not a technician, but I see this question come up from time to time.
I've noticed that because the techs recommend timing chain and rail guide replacement on the V8's every 100-120,000 miles, or so, that everybody naturally assumes it is also recommended on the inline 6's, as well.
But everytime this question comes up, the answer is always the same. Timing chain replacement on M103's and M104's is not needed. They never do it. The chains are very short and don't stretch like on the V8's.
Do a search and you'll see what I mean.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".