Wiper Question

[Walt Ebie]

Here's a shot of the wiper on my '30 coupe. It's operated by a push-pull knob on the inside but doesn't work continuously. That is, when you pull the knob it will wipe to one side and stop. Push the knob and it wipes back to the other side and stops. Won't keep on wiping. Your thoughts? I use Rain-X and don't go out in the rain anyway so it's not a major problem, I'd just like the wipers to work the way they are supposed to. Any help would be appreciated.