Hi Stephan,
Eduard Ritter von Schleich did fly combat missions in WW2 as the Wing commander of JG26. This occured during the period of September to December 1939. I can tell you with confidence that he did not score any confirmed victories while with this unit. There is evidence though that he did fly with his wing on several occasions during this period. He was always someone who liked to "mix it up" with an enemy. JG26 was stationed on the Northwest portion of Germany at this time, and their primary mission was air defence of the western frontier. Because of this, they did not see too much action.
Try 'Ritter von Schleich' by Fried Lange, or 'Der Schwarze Ritter' by Schenzinger (both written in German; sorry no translation available) for in depth information on von Schleich's flying career during WWI and into the 1930's. Unfortunately, not much has been published specifically on von Schleich since these two books came out in the 1930's. But you can find his name popping up in a large variety of books on WWI aviation. I find him to be most fascinating.
regards