Acrylic bathtub small crack
I don't know if you checked with Kohler on this but they have a lifetime warranty on acrylic/plastic tub surfaces if you are the original owner. Depending on the nature/cause of the damage you might be able to get it covered despite it's age. If they don't cover it they may still be able to help you with advice on a method of repair. Give it a shot.
Here's a link: https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/1353553-12.pdf