Update to my last post: the Timberland Boot Kit helped a bit, with a few cycles of brushing and cleaner and then conditioner. But what ultimately helped most was dried bread. :
Timberland Boot Sauce Conditioner in Neutral in Neutral
Amazon.com: Timberland Boot Kit Shoe Care Product Set, No No Color, One Size Regular US : Clothing, Shoes & Jewelry
Timberland | How To: Clean + Protect Your Timberlands