Rotate your cylinders
If downtime is an absolute impossibility, you may want to keep a set of spare cylinders you rotate into service on a regular basis. This will keep your cylinders fresh in spite of high risk particle contamination or extreme operating conditions. Once one cylinder is removed from service, it can be disassembled, inspected and repaired if required.
When a cylinder is in pieces, it’s a good idea to replace all seals, since they’re typically very economical. Inspecting the internals of your cylinders on a regular basis also gives you clues to the condition of the rest of your hydraulic system. The occurrence of varnish, for example, could mean your oil is running continuously hot, and you may need to address operating temperature.
Also, a physical inspection of the piston and cap can tell you if particles have been trapped within the cylinder. If it looks like someone was beating your piston with a ball peen hammer, then I can guarantee a chunk of metal has been slapping around inside for months or years. And if it made its way into your cylinder, it existed elsewhere in the system too.