That stem you are referring to is attached to a float inside the bottom of dishwasher tub. The float rises as water comes in. The float stem rests on a switch which will shut the water off when the float rises to a certain point preventing water to overflow.....if water is leaking down the stem then your switch isn't working or the float is stuck in the down position. Try pulling up on the float and see if it's stuck. Sometimes you have to clean out where the stem goes thru the tub.