I’m wondering if because you once co-signed for your daughter’s car payment they might have comingled your score with hers. The only way to find out for sure is to go to www.AnnualCreditReport.com and get a copy of your credit report — not the score, but the report — from one of he three bureaus. (All should have the same info.) It’s free and you do not have to sign up for credit monitoring. See if there are accounts you do not recognize that might have impacted your credit score.
Removing your longest-held card (who needs a Sears card anymore!) shouldn’t have that much of an impact. And your retirement shouldn’t impact your credit score eithr.
Not sure where you’re getting your score, but I would go to CreditKarma.com to get your score. You can contact them and ask why the score has declined that much. I understand your concern. Please write back and let me know their response.