Death
Death itself possesses infinite durability, having operated continuously since life first emerged. However, Death's work product - the deceased - demonstrates markedly poor longevity. Soft tissue decomposes within weeks under normal conditions, bones persist for centuries at most, and even fossilisation preserves merely a mineralised approximation of the original organism. Death's victories, whilst permanent for the individual, leave diminishing physical evidence. Within geological timescales, most deaths leave no trace whatsoever.
Lego
Lego bricks manufactured in 1963 remain fully compatible with bricks produced today, demonstrating extraordinary design consistency. The ABS plastic construction resists degradation for an estimated 1,300 years in marine environments, creating a dubious environmental legacy but unquestionable durability. Archaeologists of future millennia will unearth pristine Lego bricks long after the bones of their owners have returned to dust. The clutch power of a properly manufactured brick - the force required to separate two connected elements - remains constant across decades of use.