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 Cleaning Tutorial - YouTube
Timberland Boot Cleaner Walmart Sale, 52% OFF | www.colegiogamarra.com
Timberland | Shoes | Men Timberland Boots Wheat W Shoe Cleaner | Poshmark
Men's Accessories For Sale - Product Care & More
How to Clean Timberland Boots (with Pictures) - wikiHow