two piece exhaust manifold leaking at joint
 

1999,f650, with Cummins 5,9l leaking at expansion joint on the two piece exhaust manifold. Called Cummins dealer and he had said something about a sealant that could go in the joint? He didn't know the part # but told me he would call back with the # but he never did. Does anyone have a fix for this problem?

The only sealant I can think of is High Temp Silicone, but I doubt it would last very long. Some of the 2 piece exh manifolds on our Deere engines use metal seals. They are like a keychain design, but about 3 wide of a thin spring metal.
How much does it leak, cold or hot?

Leaks enough to put soot on side of engine and the truck is very weak when pulling.