Heys guys I need help in locating someone or somewhere who has a third seat fro the W123 station wagon (1984). Thanks a lot.

You can buy these from aftermarket suppliers at a fraction of the dealer cost. I installed one myself about 8 years ago, it was easy to install and had perfectly matching MB Tex. The only difference is that mine doesn't have the shoulder harness seat belt, only lap belts. If you want the full shoulder harness you need to replace both the rear front side panels and add anchor points in the headliner. Given the fact we only use the seat occasionally I don't see it as a problem and think the lap belts are sufficent. I found my seat from an ad in Hemmings Motor News, an outfit in Georgia I believe (it was a long time ago).

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold