Every petition for reassessment filed under Section 11338 or Section 11339 shall be in writing and shall state the specific grounds upon which the petition is founded. The petition shall include a statement of the petitioner’s opinion of value of the private railroad cars assessed.

Any petition that does not meet the requirements of this section shall be deemed invalid and shall not be acted upon by the board. A petition timely filed but deemed invalid may be amended or supplemented and refiled within such time as the board may prescribe; provided, however, that no amendment of a petition filed under Section

11338 may be filed later than December 31.