No savings bank or savings and loan association shall invest in or make loans to any service corporation or subsidiary thereof after the effective date of this Part, unless and until the parent institution has executed and filed with the superintendent a letter agreement which (a) states that the service corporation is subject to the general supervision of the department, (b) permits periodic examinations of the service corporation and/or any subsidiary thereof, as the superintendent deems necessary, and (c) states that the parent institution will reimburse the department for the total cost of such examinations.