Blocked external shower

I believe that is actually a vacuum breaker or the like. When I changed my OEM outside shower to a sink sprayer nozzle instead, I was able to simply unscrew that part and thread a brass adapter directly into the fixture. ST

I would drill and flush.

Try Ace Hardware for a replacement washer. They usually have quite a selection.

I fixed it, but it's now leaking slightly. I stopped at Walmart, but the only thing they had was an assortment of washers, and none of them was an exact match.

It appears to just be a manufacturing mistake. Drill it out.

Gary,

That is different than a residential fixture, but the idea is the same. It is as good as the change in daylight savings time and ethanol in motor fuel. It was part of the same congressional energy saving. It is supposed to limit the flow of a shower to 1.5 GPM. But there is a problem and frequently the rubber plug that is supposed to deform and maintain that flow gets deformed and does as yours is.

You might be able to pull that plug out and replace it or the fitting. You can't leave it out because that would be defying a congressional edict.

Matt