Though the overall quality of Mercedes Benz vehicles is second to none, occasionally problems occur, as with any vehicle on the market. There are a few instances in which water leaks have occurred in particular models. These leaks are the exception, not the norm. Do your research before purchasing any vehicle, particularly a used vehicle.
Some owners of the Mercedes W220 have noted problems with water dripping from below the glove box of the passenger side when it rains or when the vehicle is washed. In some cases this was an indication of a clogged drain. Access the drain by opening the bonnet, locating the plastic grate covering the fresh air intake, removing this grate and cleaning out the leaves and other sediment.
Some owners of the Mercedes ML320 have complained of water dripping from the skylight on the driver's side seat. This may indicate clogged sunroof drains or a poor seal, as is common on many sunroofs from many manufactures. Pour water in your sunroof drain to see where it exits and repair damaged seals with RTV silicone.
In some cases, wind shield wiper fluid has been known to leak when refilled from near the passenger side wheel well. This may indicate a cracked wiper fluid compartment or simply overfilling of the fluid. Consult your owner's manual for recommendations on how often to fill or have your service technician determine whether a replacement of the compartment.