When you replace the inlet manifold gasket on a Discovery 3.9 v8i, should you use any form of sealant between the gasket and the heads or inlet manifold?

The old one did not seem to have anything on it, and the workshop manuals and Haynes make no mention of it, but I am beginning to wonder...

You dont need any sealant arount the inlet ports, but the manual suggests that you should apply sealant where the gasket transitions from the head to the valley.

When I did mine I used Hylomar and ran it around the water ports also because I am paranoid about water leaks

are you using the latter black foam covered gasket then as stated apply some hylomar blue sealer around the water ports ensure the manifold is clean and free from heavy corrosion around the ports.
from 1994/5 model onwards the procedure for the fitting of the manifold changed and required three stages of torquing down to ensure a good seal is made.
I also apply a very small drop of stud lock to the manifold bolts as well as i have had them work loose
the stages are
working in a oposite to oposite in a clockwise motion torque the bolts down
stage one 10nm leave for 5 min
stage two 30 nm leave for 5 min
stage three 54nm

The gasket I had was sheet metal, no foam, no composite sections. And I used no sealant. I followed the torquing stages suggested, but didn't know the thread lock trick.