Yes you do. The distributor must be removed.
Intake manifold gasket
There is a tapped hole next to the distributor hole in the intake manifold.
Yes.
Possibly lithium grease or condensation
It depends on the engine size. Some are located on the side of the engine block and some are under the intake manifold.
No.
Under the intake
I'm having my 1999 Suburbans done for around $600 this includes an oil change and tune up.
On a small block Chevy the distributor goes through a hole in the intake manifold. On a Pontiac the distributor goes behind the intake manifold.
under the intake
The intake manifold.
It is located under the upper intake manifold.