"1. Can it remain the way it is?"

You vary well may end up with mildew/mold inside or at the very least nasty water stains. So I would get them on it before the warranty period is over and the repair is on your dime.

https://www.homedepot.com/p/Hy-Lite-47-in-x-47-in-Acrylic-Block-Fixed-Vinyl-Window-in-White-9PW4747WHV1500W/202338958

It's a fixed unit. No way to replace individual blocks. Replacement is the only option. But given that this one has failed in multiple places, I would replace it with a real window.

And get a proper bathroom exhaust fan installed ASAP.

Gee, I thought I had successfully deleted my question when I wasn't getting any replies, so that's why I haven't been checking Houzz at all. Thanks for taking the time to answer.

Millworkman, what do you mean about the warranty? I'm not aware of any warranty on our windows. Wouldn't have any idea how to look into it.

And cilantro, are you saying we should get a different type of window? I wish it weren't so large, but being a brick house, I guess we're stuck with it. I'd rather have a large shower in that spot with a small window for ventilation only.

I made an assumption, possibly incorrectly that this was new construction and that was the warranty I was referring to. A builders warranty but if this is an older house (more than a couple years) or you are not the original owner that ship has long since passed.

ci_lantro may be correct as well that that is not individual block but a complete prefab unit. So there is that. I would stop by a HD or Lowes and see what is available in glass block interior units.

I wish it weren't so large, but being a brick house, I guess we're stuck with it.

Is it possible to match the brick?

If not, one idea (I've never done this) would be to install a smaller window and flank it with shutters to cover the fill-in. Add a flower box to the bottom if you want a shorter window. This would be totally acceptable to me IF the window in question faces the backyard. Would work streetside, too, if you have shutters on other windows.

Another make-do approach might be to install a smaller window and add a Bahama shutter to cover the original window opening...

Yes, I would get a different window. This one has failed & it would be reasonable to assume the next one will fail eventually, too. Plus, your stated wish to have an operating window for ventilation.

ETA that this leaky window almost certainly doesn't match the rest of the windows in the house anyway. [That it doesn't match the other windows helps make the case for a make do (adding shutters, window boxes, etc.) or whatever else you can come up with regarding smaller window/ adding a shower...]

One other thought under the heading of Project Creep ;-)

Is there any place where you can steal enough bricks to fill in around a smaller window?

Like any brick columns? (Replace the brick columns w/ some other material.) Do you want a taller window someplace? Want to add another exterior door? Assuming a full brick house, steal some bricks from the back wall of the garage and make it some kind of feature. Or cover it up w/ a lean to garden tool storage shed.... i.e., start thinking outside the box.

What's sad is that when we moved in, there was a pile of bricks in our backyard stacked on a cement drain. At least 100. We let an elderly neighbor take them to build brick walkways and walls in her backyard. (At 88 years old, it was her hobby.) But putting shutters up might work. We're in a small subdivision with a pretty strict HOA, but we have a row of shrubs along the side of the house which partially cover the window.

Glass block windows (without moisture inside) have a stated R-value of about 2. With moisture inside, its going to be less than that, probably a lot less. Normal windows with low-e glass have an R-value of 3 and up. How about ordering a replacement window with low-e glass anda coating and just replace the glass block window?

Formulaross, that's what I'd like to do. Guess I'll have to start looking for a window company.

If you want a shower there, I would make this into a high clerestory window above the shower. Your picture does not show the whole wall, so I don't know if it is already that high. If it is not, the bricks removed from the area for the high window could be used in a design with other, contrasting bricks, to fill in where the window had been.

If you do not have a neighbor whose windows look into this area, this high window could be clear glass and allow in a lot of light. Clerestory windows that let you see tops of trees or views of mountains are especially nice.