Features on 1985 300TD wagon (S123)
In W124s is very easy to tell the difference: the stitching on the seats is different (M.B. Tex is vertical at the backrest, Leather is horizontal). On the W123s is more difficult to tell the difference, usually leather ages poorly compared to M.B. Tex, with more cracks and color tone variations in certain areas.
Yes, the holes on the back seat are for the headrests. It all depended on the market: but basically all W123 wagons came standard wih a full rear bench seat with no headrests and no third seat. In the early days, you could order the rear headrests (2 or 3) as an extra. If you had the rear facing seat ordered, 3 headrests were installed automatically. In the last days of production, most markets had the 3 rear headrests installed as standard.
The 2/3 split rear bench was an extra available on last production models. Interesting fact: rear seat headrests are adjustable in angle when there is no rear facing seat installed. If a rear facing seat is intalled, the headrests are fix at the upright position.
In Germany and most markets there were four seat upholstery materials: cloth (standar), M.B.-Tex (little extra cost), Leather (Expensive extra cost) and Velour (HyperExpensive option).
W123 Wagons in the States were fitted standard with M.B.-Tex a VERY FEW were delivered with leather (due to the high cost of the option).
Some interesting options were: headlight washers and wipers (for Euro headlights), sunroof (ONLY manual, M.B. engineers never figure out a way to install a sunroof motor for the wagon), and 15-inch wheels with higher ratio rear differential. The auto A/C, power locks, power windows, and 4-speaker radio that were standard in the U.S. were options everywhere else.
The W123s and S123 (wagon) never had electric front seats installed (standard nor as an option). Neither were electric outside rearview mirrors adn adjustable steering wheel.