Retired faculty members or employees of the University of Washington or Washington State University, who have reached age sixty-five or are disabled from further service as of June 10, 1971, who at the time of retirement or disability were not eligible for federal old age, survivors, or disability benefit payments (social security), and who are receiving retirement income on July 1, 1970 pursuant to RCW 28B.10.400, shall, upon application approved by the board of regents of the institution retired from, receive an additional pension of three dollars per month for each year of full time service at such institution, including military leave. For periods of service that are less than full time service, the monthly rate of the pension shall be prorated accordingly to include such periods of service.