A third update that works better as new post since it’s a new day:
The radiator housing crack was a miscommunication between the person inspecting my car and the person I was talking to on the phone. Turns out a single pipe going into the radiator was the problem and it only costs $30 to replace. They still double-checked the radiator, too,
since this little misunderstanding cost them some potential cash from me just to be sure things were OK no problems were found. Final cost: unknown since the invoicing wasn’t finished when I called, but definitely less than $875 and probably by a lot.