Mercury - Rubber Bushing Alpha One / MR / R Drive Series Durable Marine Rubber 99291T. Overview. Any boater who spends real time on the water knows how much the small parts matter. You feel it when the shift is smooth, the ride is steady, and the whole driveline just works the way it should. That kind of confidence comes from trusting components that quietly take the beating of every wave, every turn, and every long run back to the marina. The Mercury Marine part number 99291T Rubber Bushing is