Stainless steel is going to rust no matter what. Even SS screws and bolts will eventually rust. I once heard someone say, "That's why they call it stain-LESS and not Stain-FREE steel". A lifetime guarantee is still lifetime, so absolutely pursue Windline on the warranty.
Here is an exerpt from their site: https://windline.com/index.php?act=faq
If I do encounter a problem with a Windline product, what should I do?
- Answer: Because of Windline's meticulous manufacturing processes, we feel you should only have to buy it once. If it fails or wears out, Windline will repair or replace the product free of charge. In addition, customers are welcome to call Windline directly for technical support. Please call for details. PLEASE NOTE: This offer will not apply to any product that has been improperly installed, subject to misuse, negligence, accident, or has been designed, altered or previously repaired by others. This replacement policy/warranty applies only to material or labor defects. Breakage from loads in excess of the recommended load limits is specifically exempt. Implied warranties, if any, are applicable to material and labor defects as well as to wear or breakage during normal use. Windline reserves the right to examine and test the product and to make the final determination on the cause of damage to the part. Windline shall not be liable in tort or contract for any expenses, loss or damage, direct, incidental or consequential, and expect as the law produces is responsible only to replace or repair the defective product as stated above.