I have a question about slander concerning our small business.?

In short, my husband and I have just bought out his partner in their small business. There were many disagreements, but all contracts were signed and funds dispersed. In the contract both partners released each from any and all liabilities and my husbands partner (do to previous actions, this was necessary) signed and agreed to not knowingly or intentionally damage or destroy the goodwill and esteem of the Company or Buyer with its suppliers, employees, patrons, customers, and others who may at any time have or have had business relations with the Company or Buyer. and will not reveal to suppliers, employees, patrons, customers, and others who may at any time have or have had business relations with the Company, any dispute between Seller and Buyer. That being said, he told one of our biggest customers, in front of 4 witnesses that he had to have us buyout the company due to my husband and I embezzeling money from him and the company. Now, being that the facts are that his cousin was doing the accounting and we actually found that he was the one that was embezzeling, which is why we thought to buy the company to get rid of him, obviously, I was furious to hear this. Now, his cousin also does accounting for this large company, and now I believe they are calling him to do their work. Is there any legal repercussions that are worth spending the money for? Please, someone let me know, as I am not sure my lawyer is that agressive.