And .. aren't MEL's required to be endorsed by the manufacturer?
The Minimum Equipment List (MEL) is written by the operator!
It is based on the Master Minimum Equipment List (MMEL) which is written by a committee made up of the manufacture and operators, then approved by the regulatory agency that certifies the aircraft. The MMEL is part of the aircraft certification.
The operators MEL must be more restrictive than the MMEL.