To me, unless it's a simple fix ie. topping up with water, the default option should be recovery back to the depot with a replacement sent out (if it's a low frequency route)
It's not worth the time and effort faffing about at the side of the road trying to fix it unless you can guarantee it'll be fixed and the bus can be on it's way. You might as well just have it recovered back to somewhere you can work on it properly, with all the proper equipment.
While I don't know how much it costs per recovery, I can't imagine it's that much in comparison to having someone extra on staff
RE: Enviro 400MMC's for the X10