So I had this idea about an environmental kinda wapon, which lets you repair walls, gates and siege weapons over a small range (little more than melee range), but it will only repair like 50% of repairing by hand.
The main reason this might be useful is the fact, that once the zerg comes knocking your place down, the gate will be drowned in aoe circles, downing certain classes downright and hindering most others from even getting one repair tick through.
It could be available via some upgrade like upgraded gates or you can build a rack with something sold by the trap vendor.
It might even have its own mastery, letting it repair for 75%, farther range (to repair the oil while not dying in the wall aoe for example), second skill which channels some kind of protection for a siege weapon and its user while draining the supply. Stuff like that