RP Top Water Outlet Manifold.

[Rogerchummy]

I would have thought that some gently twisting of the manifold backwards and forwards should release the "weld" that the corrosion between the stud and the manifold has created. Worth a try before the drastic action you are contemplating. Bear in mind that if all else fails and the manifold cracks, they are readily available quite cheaply from David Cochrane at A7 Spares (david@a7c.co.uk)