Joest Racing
Merl primarily competed for Joest Racing throughout his career in the early 1980s competing in the World Sportscar Championship and Deutsche Rennsport Meisterschaft (DRM). He won the 1980 24 Hours of Daytona with Rolf Stommelen and Reinhold Joest in a Porsche 935 and placed second in 1983 DRM championship points in a Porsche 956. That same year, he also finished 4th in the 24 Hours of Le Mans.