The R230 models from 2003 to 2011 have a lot of expensive suspension issues...
The R230 chassis SL vehicles with ABC suspension are extremely expensive to maintain; as they are several years or older now. The ABC suspension is a full hydraulic set up. Not air. It has an instantaneous reacting, fully active, hydraulic oil based system with a complex line of pumps, and an even more complex hydraulic oil diverter. The pump(s), oil diverter, and the struts all are prone to major failures at this stage of its life. In the USA, these cars experience costly repairs, often costing around a stainless steel Rolex Submariner (if one can get one). When something fails, it's not uncommon for the entire system to be heavily affected due to the complexity of the system. When you replace the entire system (at great cost), it is also going experience the same degradation and wear; thus, several years after that replacement, you will need to replace the system again. This ABC suspension does have one tremendous benefit; it does have extremely good sporty response, great comfort, and very low body roll for cars of this size and weight. The ABC suspension is utilized by the higher end S-Class and SL-Class vehicles (AMG rear-wheel-drive, Maybach rear-wheel-drive, and V12 models).
There are other vehicles from the Mercedes line-up that use an all AIRMATIC suspension. An Airmatic suspension is a; passive system (not fully active suspension), driven by air struts and one singular air pump with air connection lines to all four struts, a far simpler system than the hydraulic oil system. This system is easily serviced as failures are usually single components. This system is very good in comfort; but is a passive system and thus not as immediate reacting as the ABC suspension; also in curves, the AIRMATIC will have far more body lean than the ABC suspension. Repair costs are lower than the ABC system. In the US market, the AIRMATIC suspension is standard on S Class vehicles in the 300/400/500 engine range, all-wheel-drive AMG, and all-wheel-drive Maybach; some E-Class vehicles; some C-Class vehicles as a rare option; and many of the SUVs.
Thus, the reason why R230 models are so inexpensive in the USA, is simply because the cars are extremely expensive to maintain.