I found this about Mercedes' history in rally on Wikipedia (not always a reliable source... but quick)
http://en.wikipedia.org/wiki/Mercedes-Benz_R107"From the mid 1950s to the mid 1960s Mercedes-Benz cars were seen in rally competition, initially as the legendary 300SL, then the 220SE, the 230SL and finally the 300SE. A period of around twelve years then elapsed before Mercedes-Benz cars were again seen in rallies.
In 1977 a crew comprising Andrew Cowan, Colin Malkin and Mike Broad were victorious in a W123 series 280E in the 18,000 km London to Sydney Rally and a similar 280E of Fowkes and O'Gorman came in second. The following year the 280E of Zasada and Krupa finished sixth in the African Safari Rally.
Daimler-Benz realised that its cars had the necessary durability for rallies and that with more power they could achieve further success. While other manufacturers were rallying small to medium sized cars, Daimler-Benz decided that following their experiences with the 280E, the coupe version of their 107 series was the car to use. The "SL" in SLC was supposed to stand for "sports-light" but this was not an accurate description of the long and heavy SLC coupe, at the time the flagship of the Mercedes-Benz range aimed at the upper end of the luxury market. With V8 engines it was however a fast tourer. The fixed roof of the SLC added to the body rigidity of the SL and the superb handling, together with the comfort of the long wheelbase coupe, meant that crews would suffer the minimum of fatigue over long rallies.
For 1979 the 450SLC-5.0 was homologated as a Group 4 rally car with power being increased to around 300 hp (220 kW) and further weight reductions resulted from stripped-out interiors. Three-speed automatic transmission was retained as it was considered the only Daimler-Benz unit capable of withstanding the torque of the V8. Massive factory support under the leadership of Eric Waxenberger backed the effort behind several entries in the 1979 World Rally Championship. Three each 450SLCs and 280Es were entered in the African Safari Rally and SLCs driven by Bjorn Waldegard and Hannu Mikkola led for much of the event. Mikkola and Hertz finished a close second with Cowan and Syer in a 280E in fourth and Waldegard sixth. Greater success was achieved with a clean sweep of the 5,500 km Bandama (Ivory Coast) Rally with four 450SLC-5.0s driven by Mikkola, Waldegard, Cowan and Preston taking positions 1, 2, 3 and 4 respectively.
Following the 1978 and 1979 successes, an even greater effort went into the 1980 season. The Portugal Rally resulted in a best of only fourth place for Waldegard and Thorszelius and it was becoming obvious the big SLC was not so suited to the shorter and tighter European rallies. In the 5,300 km Safari Rally where success was expected, rear suspension failures saw a best of third place to Vic Preston Junior in a 450SLC-5.0 using the newly introduced four-speed automatic transmission. In the Acropolis Rally the power of the 5 litre SLCs resulted in shredded tyres on the rocky roads with the highest placing again going to Preston this time down in fourteenth place."