how to repair a water drip on my bosch w275 water heater?

after the severe winter switched on my water heater it worked OK. But noticed a slight drip coming down one of the 3 screws of the water assembly.Removed the 3 screws to check the ring washer it looked OK but when i replaced this part of the water assembly the leak got worse. Do you think the ring washer is the problem or should i replace the water valve assembly.