Took a look at the manifold from the ground, can see two cracks, one completely around the manifold. Although welding cast iron is possible I can't see doing it with chances of it happening again. I guess this manifold wants to shrink and the more heat it sees running aggravates the problem. I tow an enclosed car trailer with this so I would expect to see more heat that running without the trailer. Took another look online and two aftermarket manifolds (BD and DPS) are available for around 400$. They are made from much better material and also beefier & reinforced and have an expansion joint in the critical area! For the agg it takes to R&R this, not doing it twice so I will buy one of these and do the swap. The new ones are also contoured for better flow and performance. On removing the old bolt, was told to run the motor up to operating temp and then start the disassembly. Can only hope is goes smoothly, RV has only 56K on it and from what I can see, all the bolts look in good shape.
BTW, I had no idea it was cracked! One day a friend of mine was standing near the RV when I started it cold, he knew right away it was cracked by the light ticking sound it made. Once the manifold warms up the cracks tend to close up somewhat so you just don't hear the exhaust leaks! Now that I know it is cracked, it makes senses that I felt it was down on power and mileage but a small amount caused by the cracks.
