You mentioned that the house is a century old - I’m assuming it was built as a single dwelling, and subdivided later.

If that’s the case, my best guess is that the basement had a problem with flooding during bad weather, so they busted holes in existing drainage pipes to allow water to drain from the basement. The leaky walls were most likely sealed when it was converted to an apartment, but… Well, drains drains are great until they back up - I would be concerned about water coming up through them in particularly bad weather.