Case requires a repair request submitted through caseknives.com. Its warranty covers defects in materials and workmanship for the life of the owner, with repair or replacement at Case's option. Misuse damage is outside the warranty but can often be repaired for a fee.
Case operates a repair request process rather than accepting unannounced returns. Submitting the request first is what gets your knife into the system with a reference attached.
The current process lives on Case's warranty and repair page, linked below.
These are two different routes at Case and it helps to know which you are on. A materials or workmanship defect is warranty work. Damage from using the knife as a pry bar is a paid repair, which Case will often still do.
Being honest about which you have will get you a faster and better answer.
Where the original is unavailable, Case may substitute a current-line knife. On an old or collectible piece that is worth thinking about before you send it: a repaired original and a current substitute are very different outcomes to a collector.
Warranty terms are set by the manufacturer and can change. The maker's own warranty page, linked below, is the authority. We repeat what it says; we do not extend it, and a retailer cannot promise coverage a manufacturer has not offered.