This is probably a totally unnecessary suggestion, but someone may not have tried it yet.
Have you tried buying several varieties of washers and swapped them around or doubled them up? If the leak is coming from the screw-together part, it "ought" to be fixable with the right washer and strong hands screwing it on.
I've seen really cheap plastic washers, and rubber ones, and polymer ones. Maybe "polymer" is just another name for plastic, but if it costs a little more and works better, the manufacturers can call it anything they want. Even "expensive" washers are a bargain if they rescue a wand or hand sprayer.
They might even have slightly different sizes and thicknesses despite all being "garden hose" washers.
I had one cheap wand that worked great until I left it out in a hard freeze with water in it. Then every crimp joint loosened up and sprayed water freely.
P.S. In the worst case you can always tape or tie some heavy plastic film around the leaking joint so the water dribbles down the hose instead of spraying in your face. I never throw away the bags that compost and bark come in, I save them for re-use.
