I discovered that a previous employer did not report my earnings back in 1986. I've been retired (at 66) for a few years now. Is it likely that that $6,000 would make a difference in my monthly Soc. Sec. check now? I have the withholding statement from the employer. The owner is now deceased but the current corp. still exists. How should I handle this?
It probably wouldn't make much of a difference, if any, in your benefit rate. It really depends on whether or not 1986 would be among your highest 35 years of work adjusted earnings (https://www.ssa.gov/pubs/EN-05-10070.pdf). If you have proof of your wages that year, ideally a W-2 form showing that FICA taxes were withheld, you can submit the proof to Social Security and request a recomputation of your benefit rate.