T. W. Manson’s The Sayings of Jesus. This book focuses on material traditionally associated with Q, M, and L. It looks to have been recently re-published.
G. R. Beasley-Murray’s Jesus and the Kingdom of God. Not quite so old as Manson. But old-fashioned enough in approach (traditional historical-critical readings) to be included here.
Another book, recommended to me by a different person:
Eta Linnemann's Parables of Jesus: Introduction and Exposition. This is from her earlier form-critical years before she rejected historical-critical method. It also represents one of the earliest monographs by a female scholar in this field.
So now I put it to you. What is an older/oldish book that should be included in a Jesus class?