The early Le Mans dual seat is a block of closed cell foam with retaining nuts molded in. It has no cover and no surface finish other than that which occurred naturally from being in contact with the mold. It also has no separate base, because it bolts directly to a one piece fiberglass part that incorporates both the rear fender and seat base. Very clever and simple to make, plus it matches the 70’s race bike esthetic along with lots of flat black paint etc.
My Le Mans with its 44 year old original seat has 100K miles, most of which were with me sitting on it, still looks good and there’s no chance I’d put anything else on it. It’s not supposed to be glossy like vinyl, that’s a distinctive part of the bike’s look and the shape is excellent: it allows you to move around and sit on your thighs and supports you under deceleration. It’s not a touring seat by design but I’ve done lots of 500 mile days on mine. The only time it ‘wore thin’ was on a 10 day long trip when we were riding all day, every day.
The later Le Mans III seat was made similarly, but with a harder foam and shinier surface that was supposed to match a move away from the race bike look. This in combination with a longer gas tank, less support for braking and thinner shape leads to a better match with the ‘upholstered 2x4’ story. It’s significantly worse in function. After that on the Le Mans 1000 they gave up, succumbed to conventionality and used a vinyl covered seat, which was also poor.
PS you can buy a new Le Mans seat but they're not particularly inexpensive. Although mine is still fine I’ve thought about buying a new one just in case they again become unavailable some day. Maybe something for next years Christmas list.https://www.mgcycle.com/index.php?main_page=product_info&products_id=2919