Water-inlet valves eventually fail. One problem that may develop with a water-inlet valve is that it can no longer completely shut off when the electricity is turned off to it. Then, the valve may leak and drip water into the clothes tub--you may notice that your washer has water in it when you haven't used it for a few days. To fix this, replace the valve.

Here's the part and where to get it: http://www.repairclinic.com/SSPartDetail...

I've used these people and they are fast and reliable.

They also carry a repair manual for it: http://www.repairclinic.com/SSPartDetail...

UPDATE 7/2020

This can also be caused by low water pressure, i.e. the hot water has been shut off at the tank, or just very low pressure.