how to remove a very short nipple for tub spout

Hello,
I'm new here-
We have determined there is a slow leak where the tub spout nipple attaches to the galvanized elbow behind the wall. That junction hopefully just needs new teflon tape and dope, etc, or a new nipple. So we'd like to get it out. Unfortunately it's a very short nipple, with just the threads protruding from the tiled wall. A two inch or so long brass piece attaches to this short nipple, the brass piece has an o-ring that seals the tub spout (Delta product from about 10 years ago).
We could change the kind of tub spout to one with a more standard 5-6" nipple, but we still need to remove the short nipple first...

How do we loosen such a short nipple? I tried the vise grips and just stripped the threads closest to the wall (there are still plenty of threads left to attach the brass bit)

I read about an internal pipe wrench. What do they look like? Would home centers carry them?

I don't want to take the wall apart if at all possible.

Thanks for your help!

Ok, the hardware store has them after all. I just needed to find an employee who'd heard of them... Wish me luck, hopefully we can stop the drip!

This would be a good time to scrape the galvanized elbow and replace with brass. I would use a brass nipple into the spout as well. Sooner or later the galvanized will start to rust.

Here you go they are also called nipple wrenches.

AFter you remove the nipple install a brass one. With that spout and brass adapter you can even use a longer one. DO NOT discard that spout and adapter because it is a MUCH better one than one of the "conventional" spouts you were planning to replace it with.

thanks for your help!

We bought the nipple extractor, got the old one out,
cleaned the elbow and put the new brass nipple in...

The hardest part was getting the old nipple off of the nipple wrench.
(We ended up tapping it with a screwdriver.)

Success! but... the elbow was dry when we had it apart.
so that wasn't the problem :(

So there is still a drip. Only during showers, not baths.
We're adding caulk today around the faucet handles.
And we'll seal the grout (again) - even though I doubt that's the problem.

Everything else we can see from the access panel is dry.

90% of the time the leak is in the tub's overflow gasket. When you shower some water splashes into the opening and if the gasket has deteriorated, like most of them have, it will then leak into the ceiling below. Run the water into the tub, and while it is running put your hand under the flow and direct it against the overflow plate. If that is the problem you will quickly have a leak.