I was under the impression all North American market Range Rovers had electric seats, but I guess only the Hunter edition didn't. A little research revealed that they only made 400 Hunters in 1991, which is probably why replacement seats are so rare:
Britain's Range Rover has come down the mountain for 1991 with a ``no-frills'' but still elegant version of its luxury sport-utility vehicle that has been carving a small niche among affluent Americans since 1987.<br> Range Rover says its ``Hunter'' edition is intended for ``value-minded'' …
www.deseret.com
If it helps, you could remove the seats; refer to page 679 (page 34 under Body) in RAVE
With some access to the bottom side, you might be able to identify what's wrong