in 2013, fia gt3 european championship was merged with fia gt1 world championship to form fia gt series, where buhk continued to race. he was paired with alon day in htp motorsport, they was victorious at zandvoort, but was only seventh in the championship. he remained in the adac gt masters where he participated with maximilian götz. they won race at nürburgring and ended third in the standings. also he expanded his programme to compete in the blancpain endurance series. despite missing two opening rounds, he won 2013 24 hours of spa as well as the season finale at nürburgring, which brought him title in the series.