What kinds of contractors deal with basement/foundation flooding/leaks?
Just for future readers, I ended up bringing in structural engineers who found my basement wall was bowing from the stress of the soil outside the house (becomming water-logged, freezing, expanding, etc.). This was also the cause of the vertical crack/fissure that opened up, which was my chief complaint in the original question above.

The solution they sold me on was to bring in 5 heavy-duty steel I-beams and anchor them between the basement floor and the rafters above. $2700 after everything.