Returns the amount (1 is full) of repair resources in the cargo space of a repair vehicle.
Note
Since Arma 3 v1.96 the return value for vehicles that are not configured to have ability to repair other vehicles is -1. (Prior to that the value was negative infinity)
The repair cargo does actually reduce when a repair truck repairs something, however, the default cargo amount of 1 is so high it is functionally infinite. It's inconceivable that you would drain the pool. You would need to set the cargo to 10^-5 or 10^-6 (0.000001 or 0.0000001) before it is low enough to "realistically" run out given how physically large the storage pods on the trucks are