I will retire from teaching after 25 years in a system that did not take out SS. I am divorced and was married 27 years. I think I can get half of my ex-spouses benefits but I am not sure. If so, will it be reduced by the Windfall Tax or GPO? If I work the last 5 years at a job that does take out SS, will the Winfall/GPO be eliminated from my benefits?
Yes, if you're receiving a pension from a government employer in the U.S. where your wages were exempt from Social Security taxes, any divorced spousal or widower's that you become entitled to from Social Security would be reduced by 2/3rds of the gross amount of your non-covered pension. This is due to the Government Pension Offset (GPO) provision: https://www.ssa.gov/pubs/EN-05-10007.pdf.
It wouldn't matter if you work somewhere else and pay into Social Security for 5 years or more. The 5-year GPO exception applies to people receiving pensions based on a combination of covered and non-covered work. If the last 5 years of work on which the person's pension is based was subject to Social Security taxes, then the pension may be exempt from GPO. For more information on this and other exceptions to GPO, refer to this reference from Social Security's handbook: https://www.ssa.gov/OP_Home%2Fhandbook/handbook.18/handbook-1836.html.