Mercedes-Benz W204 rear subframe rust and bushings
Mercedes-Benz W204: why does the rear subframe rust and how is it prevented?
The open end of the subframe lets moisture and dirt in behind the bushing, and the subframe can also rust from the inside. It should be cleaned at every tyre change and protected with an oil-based protectant. Rubbery compounds are not recommended, because they keep moisture in.
Mercedes-Benz W204: what should be done if the rear subframe mounting lug is rusted or torn?
The subframe is an important part of the chassis, so have a workshop assess the rust damage and the repair method. They take into account whether the rust is only on the surface or inside the structure.
Mercedes-Benz W204: do worn rear-end bushings affect handling?
The effect varies. Worn bushings can make driving unstable and wear tyres unevenly, but some of the bushings are durable. Before replacing, check the squeak-prone control arm bushings and the front bushings of the subframe; the repair is often done by replacing them, and after that the car is aligned.