Leaking From Handle
There are 2 possible reasons for the F501-3-1 to be leaking from under the handle. The first and most common reason is that the cartridge securing nut (part # 3 on the link below) is loose. This means for cartridge isn't being held in place and water is pushing through the top.
The second possible cause would be there is debris in the cartridge. This can be from hard water or from recent pipe work elsewhere in the house. To flush out the cartridge follow the steps below: F501-3-1 parts breakdown
1. remove handle set screw
2. remove handle - this will just pull off.
3. unscrew dress ring by hand.
4. unscrew cartridge securing nut with wrench.
5. remove cartridge and flush out any debris.