(a)
(1) No letter of attorney, duly acknowledged or proved and certified as prescribed by this act, shall be revoked but by the maker of the letter of attorney or his or her legal representatives.
(2) The revocation shall be in writing acknowledged or proved before the proper court or officer and filed for record in the county or counties where the letter of attorney was intended to operate.
(b) All such letters of attorney shall be revoked and deemed void from the time of filing revocations for record.