Forget it, this is obviously beyond my cerebral understanding. Casually moving on...
I have yet another curiosity (throw me out the window), this time involving the interior. My car has these strange half-MB-Tex, half-"zig-zag" cloth pattern seats, and I have never seen them on any other W123. Could these have been some special order item that was never officially sold? I want to think that this car is unique, and not just your everyday run-of-the-mill 240D-like car. How about this: does the interior combination of Palomino base/"hybrid" seats/black plastic interior paneling and trim/top-loader washer correspond with the Euro 200 model of July 28, 1981? Is this a standard interior option combination for that model? Questions are asked because my logic follows "Knowledge is power, or at least understanding".
Does anyone have any ideas on what to replace my decomposing horsehair seat mats with? I have the seats apart right now to fix the fact that they have gone 'flat' and are somewhat uncomfortable.
The interior pattern that you have show in not "strange". This is the standard interior found on all 123's worldwide except for the US where we had MB-tex as standard. The pattern you have is referred to as "Herringbone" and was available as standard on the 2nd series 123's. Essentially from 1980-1982/1983. This included MB-tex on the outsides and cloth pattern inserts.
The early 0.5 and 1st series 123's had interiors like what Nutz 4 Benz has shown. He's correct in that they're referred to as "Houndstooth" pattern and they also had the "bat ear" style headrests. The MB-tex part of the seats had a different grain pattern that closely resembles little pebbles.
3rd series 123's came with seats that were mostly cloth o the seat back and seat bottoms.
Your car also displays the "low spec" European headlights. All 280 models came with the high spec squared Bosch or Hella lights.
Another clue that your car was not a 280E originally does involve with your seat pattern style. During production (true for 1st and 2nd series models), the Coupe models and the 280E's were regarded as the top-of-the-line models and to differentiate them from the "lowly" models, they had a different insert pattern. The Herringbone was standard for models, even for the 280TE model which is also considered their high end 123 model. The coupe and 280E's came with a square pattern insert.