The sealing ring of the chain tensioner starts to let through, and engine oil escapes at the tensioner. The cause is insufficient manufacturing tolerance of the sealing rings. Beyond the loss of oil the chain tensioner can also loosen, and in an extreme case the timing chain comes free, which means engine damage. A separate phenomenon is that on the early OM651 engines a shortcoming of the tensioner let the chain stretch prematurely, which typically caused serious engine damage. The maker revised the tensioner several times, so this mainly affects the older units. The maker issued a recall, for more than 100,000 cars in Germany and for 2,869 cars and 2,579 vans in Austria. The range is the four-cylinder diesel units built between February and November 2014. The classes affected are A, B, C, E, S, V, CLA, GLA, GLK, SLK, CLS, ML, GL, Vito, Viano and Sprinter. It also affects older cars that received a replacement engine or chain tensioner from that period. The repair is replacing the sealing ring, free of charge under the campaign, and takes 1.5 to 2.5 hours of workshop time. The visible sign is an oil trace at the rear of the engine.