I think your brake fluid was boiling. When it boils it is vapor and hence no brake. It could be one of the followings:

1) The caliper got hot when you were in heavy stop and go traffic.
2) The other reason could be your brake is binding and the caliper got hot, hence the fluid boils.
3) You have contamination in your fluid which lowers the boiling point.

Check the calipers and then flush all brake fluid. It has to be seen to.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
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