You did the correct thing by hiring an attorney to write your demand letters. The complexity of what your former "partner" did is beyond a public forum. An attorney can advise you on your strategy to "help me bring a stronger case" but on your facts I am not sure what needs to be stronger. You may have several different claims, including but not limited to breach of fiduciary duty.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
You have to take your partner to court to force an accounting and distribution of the assets according to the OA agreement. It probably will require an an appraisal.
Disclaimer of California Attorney. Laws differ from state to state. Although the above response is believed to be accurate, it should not be relied upon as any type of legal advice because the information provided is incomplete. It is intended to educate the reader and a more definite answer should be based on a consultation with a lawyer. No attorney client relation is formed with me without a written contract. Good Luck starts with a strategy and a plan. Robert J. Suhajda, MS,CPA Attorney-At-Law 17721 Norwalk Blvd. #43 Artesia, CA 90701 562-924-8922 Tax Relief Lawyer. Former financial auditor and controller. Admitted to US Tax Court, Income Tax, IRS representation, Fiduciary income tax returns, Estate and Gift tax returns, Homeowner Association Strategist.
In your question you mention "our lawyers." Do you already have a lawyer to represent you personally or does the lawyer represent the LLC? I agree that you would be best served by an attorney to represent your personal interests.