Leslie expanded the opportunities of PM in 1936 and created the A-D Gallery. This provided another opportunity for artists to be seen by the inner circles of the advertising and printing world. The name PM was sold in 1940 and the magazine

Percy Seitlin and Dr. Leslie, 1942, co-editors of PM and A-D Magazine. Photo appeared in the final issue of A-D, April/May 1942. photo: Alfred A. Cohn

continued under the name A-D magazine. In 1942 publication was stopped as the United States entered World War II. During the course of its run, the magazine was to feature hundreds of artists and helped to launch and expand the careers of many, including several european emigres. During the war, Dr. Leslie was with the Office of Information Service . In 1949 he travelled to Israel for the first of many annual trips. Throughout the forties and early fifties he was active in the business and as director of The A-D Gallery. In 1958 the gallery was reactivated as Gallery 303 and in 1965 became host to the lecture series "Heritage of the Graphic Arts." The gallery presented over 200 lectures in that series and in 1972 several were collected into a volume called Heritage of the Graphic Arts.

In 1965 Sol Cantor died, thus ending a 40 year partnership. In 1969 Dr. Leslie retired as president of The Composing Room and was awarded the AIGA medal. In 1971 he worked extensively to help set up Uncle Bob's Paper Mill in Israel and in 1973 he received the Goudy award from RIT.