Leaking Washing Machine Shut Off Valve
Definitely packing. Can't 100% confirm from the picture whether it was designed to be serviced, but there has got to be a reason for the hex-shaped machined valve bonnet. I think you need to use bigger wrenches (back-up wrench and working wrench) and get that bonnet off so you can repack the valve. It's likely just stuck.

I would just cut it off or "un-solder" it and replace it with a top quality ball valve.