The SRS light was on as descibed by bbrewer, ON for about 2 minutes on my 140. The fix as to replace the passenger's seat belt. I also choice not to repair.
It light was off for a few days, I beleive the tech reset the code, after the seat belt was used a few time, the computer detect the problem, and turn the light on again.
Anyway, I call 1-800-formerecdes, they pay for parts, and I pay labor charge to replace the seat belts.