The rear shocks are interchangible from 123 and 126 I believe. the air shocks will ruin the ride of a benz I suspect.

Unless the rear is really sagged I would just let it sit down a bit and allow the suspension to do its job. You may be able to redistribute your load in the trailer a bit to lighten the tongue load.

These cars are designed to handle a load. You won't hurt them as long as you follow the guidelines in the owners manual.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.