If your blender jar is leaking, check the following:
(1) Is the sealing ring over the blade?
(2) Is the bottom cap on tight enough?
(3) Is the jar cracked at the bottom?
(4) Is the bottom cap cracked?
(5) Is the sealing ring missing?
(6) Is the sealing ring cracked, broken or rotting?
(7) Does the item being blended exceed jar capacity?