If your silo is still being used for feed storage, we recommend that all cable pulleys be oiled once a year. Also that door hinges be oiled annually as well. This simple procedure can avoid many costly repairs.
After the silo is filled, the top of the wall can be scraped off prolonging the life of the roof.
The single biggest thing that can be done to preserve the life of the silo is to make it a practice of having ensilage dry enough that the juice will not run.
Keeping chute clean and bottom of silo exterior clear of rotting feed will also be a big step in silo preservation.
For other excellent silo advice, read Silo Sense by the International Silo Association.