I read three of the Alex Kane novels at least 30 years ago. I couldn't tell you the titles anymore. The basic plot of one involved an 18-year-old gymnast who needed rescuing from someone who got him hooked on drugs and was pimping him out, and the plot of another involved exploitation of gay senior citizens (which might still be relevant).
I went to check the titles in my library and found an empty space on the shelf. Then I remembered that earlier this year I included them in a collection of books I donated because I didn't expect to read them anymore.
Now, of course, since I decided to put together a collection of Preston's works, I wish I'd kept them--and might even want to read them again.
It figures. ...
Edit to Add. Much to my surprise, a surprising number of Preston's books are listed on eBay, so many that I think you would have to search for a specific title. It appears the Alex Kane story about the exploitation of gay seniors is
Golden Years.