The rear bushing of the lower control arm is hydraulic like the motor mounts. MB has done this to soften the road vibration that comes through the chassis. They used to use a separate subframe to absorb. As with the motor mounts these bushings work great when new but fail much quicker than hard rubber. MB parts system says that there is a new number for the original part and the old number is no longer to be used.
This usually means they have improved the part. I didn't see any service bulletins but I didn't look very hard.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician