Quicksilver - Cylinder Bore Seal Engine Sealing Components Precision Fit Design 8597721. Overview. Anyone who has spent enough time running a Mercury outboard knows how much trust you place in the internal seals. They're hidden away, doing quiet work, yet they make the difference between an engine that pulls hard and one that feels tired. This Quicksilver cylinder bore seal has that dependable, reassuring feel - the kind of part you install once and forget about because it simply does its job ev