Section 8. Notwithstanding the failure of the owner of a motor vehicle on which an excise was assessed under this chapter to apply for an abatement within the time set forth in section 2, the board of assessors may abate the whole, or any part of any such excise, or any interest thereon or costs relative thereto, that remains unpaid where, in the assessors' opinion it should be abated. No such abatements shall be granted unless they are in accordance with such rules, regulations and guidelines as the commissioner of revenue may prescribe and no interest shall be due in connection with any such abatement. Whenever an abatement is granted under this section, the assessors shall enter the same in their record of abatements. The assessors shall annually, not later than August 1, report to the commissioner, in the form and manner prescribed by him, the abatements granted during the prior fiscal year.