The present invention is directed towards sealable and repositionable endovascular implant grafts, and methods for their use for the treatment of aortic aneurysms and other structural vascular defects. Sealable, repositionable endograft systems for placement in a blood vessel are disclosed, in which endograft implants with circumferential sealable collars and variable sealing devices upon deployment achieve a desired controllable seal between the collar and the vessel's inner wall. Embodiments of endovascular implants according to the present invention may further be provided with retractable retention tines or other retention devices allowing an implant to be repositioned before final deployment. An endograft system according to the present invention further comprises a delivery catheter to allow placement through a peripheral arteriotomy site, and of sufficient length to allow advancement into the thoracic or abdominal aorta.