(a) At retirement a member's credited service shall include service rendered by him under the state board of control for vocational education, to the same extent that such service would have been credited had it been rendered in a position covered under this act, if the member (1) relinquishes for himself and his beneficiary all rights in and to a retirement allowance under the provisions of Act No. 136 of the Public Acts of 1945, as amended, being sections 38.201 to 38.356 of the Compiled Laws of 1948, and (2) pays into the employees' savings fund the contributions, together with regular interest, he would have paid had such service been rendered in a position covered under this act.

    (b) At retirement a member's credited service shall include service rendered by him in a position covered under Act No. 136 of the Public Acts of 1945, as amended, to the same extent that such service would have been credited had it been rendered in a position covered under this act, but such service credit shall not include any period of service for which the member has acquired or could have acquired entitlement to an annuity, pension or retirement allowance payable to or to be payable by a retirement system, except the federal social security old-age, survivors and disability insurance program, under which the political subdivision covers its employees, and if the member (1) relinquishes for himself and his beneficiary all rights in and to a retirement allowance under the provisions of Act No. 136 of the Public Acts of 1945, as amended, and (2) pays into the employees' savings fund the contributions, together with regular interest, he would have paid had such service been rendered in a position covered under this act.