Well stated CP.
That valve is traditional style and even if a Chinese knock-off is of far higher quality than the brass ball valves suggested as replacements.
The OP has probably given up in disgust since he asked for oranges and has mostly received combination wrenches for answers or suggestions, but his reference to it being stiff does indicate that it needs servicing. It is difficult to confirm by the photo but it is almost certainly a tapered plug, not all plug valves have a taper extreme enough to be immediately obvious.
The size of the flats where the handle attaches preclude modifying the sheet metal handle of a Home Depot ball valve. There is not enough material to open out and fit the flats and the material itself is too light in any event.
If the OP has not yet tried it, he needs to hold the handle end of the valve with a wrench while carefully loosening the lock nut on the other side, then carefully backing off very slightly the adjusting nut under it. A gentle tap on the handle end will loosen the plug, a shot of grease while the valve is in the open position and a few rotations will free up the valve. Reverse the procedure to finish the job but only tighten the adusting nut until movement is smooth but firm pressure is needed to rotate the handle and there are no leaks. If it leaks at all, it almost certainly needs lapping to seal correctly.
I'll look around for a picture of my girlfriend sitting on the foredeck while I repair a plug valve.