2. Banks and savings banks may avail themselves of the services of bank service corporations, and may invest in bank service corporations, but no such investment shall be made
(a) by a bank, at any time when the total of all the bank's investments in such corporation or corporations exceeds, or if the making of such an investment would cause such total to exceed, 10% of the bank's unimpaired capital stock and surplus; or
(b) by a savings bank, at any time when the total of all the savings bank's investments in such corporation or corporations exceeds, or if the making of such an investment would cause such total to exceed, 5% of the surplus of the savings bank.