I just experienced the same problem with my 300E. Light would flicker on and off. After inspecting the pads I decided to replace them. The pads I removed still had lining on them but light was indicating it was time to replace them. After replacing the pads and sensors problem was solved. Pad replacement was very easy to do. I don't think the set up is the same for the E320 but I'm sure you can follow the instructions on this site.

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Donwo
1999 SL 500 Sport (30K miles)
1998 E320 (SOLD)
1989 560SL (SOLD)
1987 300E (TOTALED)
1986 300E (SOLD)
1984 300SD (SOLD)