David Crane sketch and letter by Win Mortimer 1972

In the early seventies, a fan named Paul Goldberg wrote to a bunch of comic strip artists asking them for a sketch of their signature characters and he met with suprising success. (That likely would not happen today.) In this case, he apparently wrote to Win Mortimer and asked for a sketch of his character David Crane. Not only did he receive a nice sketch of Crane, but he also received an interesting letter from Mortimer. I would love to know what Mortimer was looking for in the strips he asked about.