Without Gernot I doubt there would have been Norisring races for so long. He had a lot of very good and worldwide connections, be it drivers or teams/owners.
He made it possible once a year that teams came over from the US to race at the 200 Meilen, Preston Henn, Momo, Danny Ongais, etc... BMW had their only works entry in Germany in 1975 at the Norisring. Porsche always brought something special, the Baby and Moby Dick in 1978. He also got the World Sportscar Championship for two years and two rounds of the Procars, too.
When Pedro Rodriguez died there he was very shaken, doubting at first if the event should go on - which it did after a rethink of the very fast track layout.
And Leistner was also known for having the idea of the Porsche Parkplatz - for many years the infield just opposite the Steintribüne was filled on raceday with up to 1500 Porsches of all types and colours (especially in the 70s).
R.I.P. Gernot Leistner.