You need a new water valve, there is a diaphragm in the water valve which regulates the flow of water. Over time the diaphragm in the valve stretchs/wears out and cannot regulate the flow. The valve is letting in too much water, more quickly than the inlet chamber can handle and the water leaks out of the breather hole.
This is a very common problem. No need to mess with the inlet chamber, just replace the water inlet valve or access valve as Bosch calls it.