We're replacing our washer so I had to turn off the laundry faucets, hook up the new washer, and then turn them back on.
In doing so, the hot water faucet now has a slight leak where the stem of the knob enters the faucet.
What are my options to fix this? Can I add any sealant around the stem? Does the stem part come off and replaceable? Or should I just relegate myself to replacing the entire thing?
Try tightening the packing nut (the hex part the stem goes through) a little. That's what it's for. Don't overdo it. The "packing" is the material that seals around the stem - the packing nut compresses that material. On a valve that is not used often, actuating the valve does commonly cause it to leak, as things have "set." Tighten a little, wait, tighten a little more, wait - try to sneak up on it, as the pressure is a balance between enough to seal and little enough that the valve turns easily.
The accepted answer is the correct way to fix the problem.
However, if there's a valve that's too corroded to turn the nut, or that isn't fixed by that solution, you can give this a try. It's not a good solution, but it works in a pinch :)
A common practice when this type of leak happens is to simply open the valve all the way, except more so. In other words, turn the knob counterclockwise until it stops, then continue to crank it counterclockwise. It can force a wider part of the metal valve stem into the metal body of the valve, and create a seal that way. You'll eventually have to repair/replace the valve, but at least you can put it off until the weekend.
