Mercury Tool-Sleeve - 91-43577. The Mercury Tool-Sleeve 91-43577 is a specialized OEM tool designed to assist in the precise alignment and installation of drive components during Mercury outboard maintenance and repairs. Crafted to exact Mercury Marine specifications, this sleeve ensures a secure fit and smooth service process when working with gearcase assemblies or related drive parts.. Key Features. OEM Precision Fit - Engineered by Mercury for exact tolerances and optimal alignment. Durable