A machine system includes a first component, a second component, and a joint assembly pivotably connecting the first and second components in a finite angular pivoting range. A boot seal seals between the first and second components, and has a rest configuration where the boot seal has a curvilinear taper, and is deformable to a squished configuration forming a radially outward bulge. The radially outward bulge stores an energy of compression of the boot seal, to bias a sealing ring in the boot seal against the second component.