When any person, firm, corporation, county, city or town holding a lien on real property upon which there is a subsequent or prior lien created by a mortgage, deed of trust or other instrument, the mortgagee or trustee therein named being dead or having otherwise  become incompetent to act, files a written application with the clerk  of the superior court of the county in which said property is located, setting forth the facts showing that said mortgagee or trustee is then dead or has become incompetent to act, the said clerk of the superior  court, upon a proper finding of fact that said mortgagee or trustee is dead or has become incompetent to act, shall enter an order appointing some suitable and competent person, firm or corporation as substitute trustee upon whom service of process may be made, and said substitute trustee shall thereupon be vested with full power and authority to defend any action instituted to foreclose said property as fully as if he had been the original mortgagee or trustee named; but the substitute trustee shall have no power to cancel said mortgage or deed of trust without the joinder of the holder of the notes secured thereby. Said application shall not be made prior to the expiration of 30 days from the date the original mortgagee or trustee becomes incompetent to act. (1941, c. 115, s. 1; 1967, c. 562, s. 2.)