Gate Valves DO NOT have a washer THEY have a disc called a GATE.
Solid and wedge and split BUT no washer.
The leak near the top by the handle sounds like the packing gland (NUT) and most of the times just tightening them slightly will stop the leak.
Other wise call a Licensed Master plumber and have him/her remove the handle screw/nut then they will back off the nut/gland CAREFULLY and remove the dangerous ASBESTOS/Graphite packing and repack this gland/nut with Code approved Teflon packing in 1/8 dia pieces installed 180 degrees apart to prevent seepage and also not pack it too tight to put undo stress on the valve stem which will cause premature failure.
Have a great one.