Many users complain that cylinder jacks leak or fail. This is primarily not caused by poor quality or product defects but it is rather a result from prolonged exposure to weather.
The jacks are made from alloy steel - even the aluminum jacks have steel components - and rubber seals. Since the jacks are primarily used and often stored exposed to weather, the steel will corrode and the seals will dry out, eventually leading to oil leakage and failure.
To extend the life of a jack, it is recommended to store the jack with the plunger/piston fully extended. This will fill the cylinders with oil, protecting the inside against oxidization and the seals from drying out. The extended piston is the only blank steel component exposed to weather. Greasing the exposed piston will keep it from corroding.