When I first saw the photo, the first thing that came to mind was that you had a leak at the drop ear 90, which is the fitting that the shower arm screws in to.

Either where the drop ear is sweated to the copper tubing coming from the valve (poor soldering), or at the threading where the shower arm screws into the drop ear 90 (cross threading, mismatched thread sizes).

Still, even if there was a leak at the drop ear 90, it should only leak when the valve is open.

You say no more water is coming out of the shower arm, so I'd let things sit as they are and see if the wall dries. However, in the meantime while you are waiting for the wall to dry, I'd remove the shower arm escutcheon and make sure that no more water is leaking where the shower arm screws in to the drop ear 90, or at the 90s' soldered joint.

Two things though...a leak at the drop ear 90 should only leak when the shower valve is open. So with the valve fully closed, if the drop ear 90 is leaking, you have a double nasty...a valve that won't fully close, and a leaky 90.

I'd even say that the previous leak might have saturated the cement board, but with redgard over the cement board, that shouldn't be a factor.

Do you know if the valve has "stops" in it? Some valves have them, some don't. "Stops" are little devices located on the hot and cold inlet ports. You use a screw driver to open or close the stop, the stop acts as an on/off valve of sorts. It allows a plumber to shut off water to the valve at the valve itself, so the valve can be worked on without having to shut off water to the entire bathroom.

If you have stops, close them. If the wall dries, excellent. Then open the stops. If water only drips out of the shower arm, then you just have a leaky valve. If the wall wets, then you probably have a valve that won't shut off and a leaky drop ear 90.

So, no real "one size fits all" cure on this one.

Mongo

Thanks, Mongo. The drop ear has a fitting to plastic tubing, so no bad sweating there. Mr. Weedy confirmed that it didn't leak when he installed it a month or so ago (he's fastidious about checking his plumbing for leaks). He said the drop ear 90 to shower arm joint was wet, and the taping/tightening on Sunday sealed it up. And he installed the finish plumbing this morning, adjusting the stops as needed. I think my somehow bumping a stop while tiling was the origination of the slow drip.

So we continue to watch the grout dry..... It just seems like it should have shown some improvement in 2 days. How long will/could it take to dry out? Is it ok to use the shower in the meantime? (My parents are arriving tomorrow.)

If that water has been dripping since the grouting was actually being done, the discoloration will probably never completely go away, and there's a better than average chance that the grout may be permanently ruined. Try hitting it with your fingernail. If it comes out, I'd score it and regrout it. Otherwise, I'd say just go ahead and use the shower.

I filed my fingernail on the discolored grout and it stayed put. We'll cross our fingers and see if it lightens up.