Maintenance is a virtual resource that can be produced in the Maintenance Depot. It is consumed by all Vehicles, as well as many of the production buildings in the game to keep things from breaking down.
When Maintenance drops below 75% there is a chance for the vehicle or building to break down, with this chance for breakdowns increasing all the way to 50% at 0 maintenance. Broken down vehicles and buildings will stop working for a period of time. While they will eventually start working again on there own, they will still be at the same level of maintenance as when they broke down, leaving them prone to breaking down again.
the broken chance are per month, if it's %50 then there is a %50 chance to break per month
The only way to refill the maintenance level of a vehicles or buildings is to craft maintenance at the depot. in an emergency, Unity can be used to repair buildings or vehicles individually by clicking on them and pressing the "Repair" button.