(2) Such agreement shall be final and conclusive on the date agreed to, and, except upon a showing of fraud or malfeasance or misrepresentation of a material fact, the question, issue or case shall not be reopened as to the matters agreed upon, and, in any action, suit or proceeding, such agreement, or any determination, assessment, collection, refund, abatement or credit made in accordance therewith shall not be annulled, modified, set aside or disregarded. [Formerly 306.720; 1969 c.520 §26]