Heat or cold, improper storage, moisture or too dry. Or simply age. The musette was discontinued many years ago so it could be just the leather got really dry. New strap will probably be between $150 and $250, but it will look new again. Far less expensive than a new bag and the musette is a great bag because it's cowhide lined. But it's definitely not free. It's normal wear and year for a bag that old. Good luck. Show us pics when she looks brand new again!