Can I sue my former boss who lied on a legal document about my termination?

I worked at a very small corporation under the umbrella of a national brokerage firm for 8 and 1/2 years. In the last year things started to change. My boss started showing signs of disinterest in his business, had several personal issues, a couple of accidents which required him to stay home. I continued to go to work every day gave up much of my PTO and kept the business running. He came in the office part time and I ran things with no incident or complaints. There was one oversight made which was actually created because my boss forged a client’s signature on a legal document and failed to do his due diligence with follow to realize his numbers were wrong. He had to compensate the client several thousand dollars to avoid further legal issues and then he tried to blame me. He would have let me go at the time to further his innocence but he kept having personal issues and needed me. After his last accident of a broken leg which required surgery, he fired me the first week after he was able to come back into the office using his own illegal actions as cause for my termination. He then made broad and untrue statements about my termination on my U5 a FINRA separation from for licensed individuals. I have 30 years of an impeccable record in the financial industry. I have tried with the brokerage firm and FINRA to have these untruths removed from my record to no avail. I do have copy of documents and proof to the defamatory statements made by my former boss but no money to bring to a court. What can I do? Is there no recourse? It seems that my former boss who is a producing Branch Manager has no supervision and he is allowed to do whatever he feels. The brokerage firm signed off on the forum even after I informed them of the illegal actions of my former boss and claim that their hands are tied. I only want the truth and my good name and reputation returned. He also fired me with only two weeks of our agreed 5 weeks PTO paid and I lost my health insurance.