Not sure what you mean by deteriorating? These gaskets are essentially a sheet of steel with gasket material either side . If it isn’t leaking don’t change it! Because of its location there is a natural tendency for all sorts of debris to gather there , if this is the case simply make a modified end for your Henry hoover .
The job itself is fairly straightforward - there are two things to need to ensure you do .
1) when you drain the coolant , ensure you remove the two block drain plugs under each bank of exhaust manifolds.
2) Take great care when you remove the inlet manifold that the valley gasket isn’t disturbed at the cylinder heads , then when you come to remove the gasket that no debris from it falls into the engine.
Good luck
