M-Class off-road problems Rear Bumper Be extremely careful when you have to cross muddy water and small mud puddles. The rear bumper is formed in a way that it scoops up the mud - that in turn creates so much drag that the thin plastic material of the bumper rips. A very similar effect is noticeable when driving off sandy ledges - the bumper scoops up so much sand that the bumper wants to stay behind.. The bumper rips apart in the three areas where the cut outs are to be found. So far there is no known cure for this design flaw. .