Members of the Board of Directors of the Association serving on the day before August 13, 1981, shall serve as an Advisory Board to the Association. A member of the Advisory Board who is not otherwise an employee of the Federal Government shall receive reimbursement for travel, subsistence, and other necessary expenses incurred in the performance of such duties. The Chairman of the Association shall serve as Chairman of the Advisory Board. Any vacancy on the Advisory Board shall be filled by the Association with a representative from the group which had a representative in the vacant position.