A member retired for service under this part whose last employment was in the California State University, as a member of the Defined Benefit Program or the Public Employees’ Retirement System, may serve as a member of the teaching staff of the California State University and shall be subject to the employment limitations as provided by the Public Employees’ Retirement Law (Part 3 (commencing with Section 20000) of Division 5 of Title 2 of the Government Code).

A person who was a member under this part on June 30, 1972, and had five or more years of service and who had attained age 55 years, shall have the option of receiving the allowance payable under Section 14245, as it read on that date in lieu of the allowance payable under subdivision (a) of Section 24202.

For the purpose of calculating retirement allowances, credit for service performed between June 30, 1956, and July 1, 1968, on a part-time basis in each school year shall be based on the ratio that service performed bears to the minimum full-time service required for credit for a year of service.

Members who were retired under a previously existing local teachers’ retirement system or the San Francisco Employees’ Retirement System prior to July 1, 1972, who have not retired under this part for the local system service performed prior to July 1, 1972, shall have that portion of the retirement allowance computed under the law in effect on June 30, 1972, whenever they retire in the future.

actuarially reduced to reflect the lump-sum amount paid under subdivision (b). The actuarial reduced unmodified allowance may be modified pursuant to Section 24300 or 24300.1.