I tried to look this up but everything seems to be related to exterior load bearing walls..

A month or so ago, we noticed a good amount of water coming through the concrete porch into our basement. This portion of the 1940's basement below the porch used to be a garage, and sometime in the 90's (according to dates on portions of the sheetrock) they put in a wall where the garage entry was to expand the living space. I don't think this was load bearing when they put in the wall.

It seems like this leak was happening in 2017 as well, since new sheetrock was added and they tried to fix it with spray foam (which is obviously not water tight and did not fix the problem).

Anyway, I ended up ripping off the sheetrock to see the damage. All four sides of the framed wall are at least partially rotted, with the top and bottom plates completely compromised on the corners. This means that I should probably replace the entire wall, which would be "easy" if it wasn't load bearing..

However, over time and possibly accelerated with water intrusion, the concrete above has a long, horizontal crack which may go through both sides. The crack doesn't line up perfectly on both sides, but it's definitely possible that it's cracked all the way through. If that's the case, it means that this wall has now become load bearing, possibly holding up a portion of the porch above.

My thinking is that I could get a jack post (or a bottle jack and 4x4 post), put it in the middle, and then build framing on both sides with pressure treated 2x6s. Then I could remove the jack, and attach blocking between the two portions of new framing.

The other, more expensive but safer option would include talking to a structural engineer. I got a quote from one, and he wanted $900 to come take a look. I can afford it, I suppose, although I'm worried that he'll end up telling me what I already know.

Pictures below. Note that this is concrete on all 4 sides, and that the drywall has now been removed from both sides.

Here's the wall:

And here's the crack on one side: