When I removed intake Manifold one of the Studs came out with the Nut. I was surprised to find that the part of the Stud that threads into the Cylinder Head has only about 4 full threads on it. So they are not an item that you would want to tighten a lot.

I saw a non-Mercedes manual that had a torque for the Manifold Bolts but cannot remember which manual or how much.

I am curious to see what the cause of the problem is as I reused my old Manifold gasket (I coated it with Copper Kote) and have had no problems with it.

Not related to Mercedes but I have twice had an experiences (on 2 different vehicles) where exhaust manifolds would not go back on easily.
The reason seemed to be that after they were removed from the Engine (no longer held down by bolts) they warped.
On the last set (from a Chevy V-6 that were off of the Engine for more than 6 monts) they were warped enough that they also need to be resurfaced.
It might be a good idea to check the Manifold surfaces with a straight edge to see if they are all still flat and lined up with each other.

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84 300D, 82 Volvo 244Gl Diesel