Jotul stoves are really nice. My parents had one in a summer cottage in Michigan. Amazing how much heat such a small stove could produce.
The best method would be to have it welded up by a shop that rebuilds heavy diesel engine blocks and heads. They wil preheat it to bright red and gas weld it with cast iron rod.
Might be expensive, or they may cut you a deal for such a simple job.
The more common way to repair it would be to gas braze it or stick weld it using a high nickle filler rod.