I maintain that the purpose of the crossfeed is so you can run both engines from one side, so why not do so?
The purpose doesn't include fuel leak. Also simply switching on Xfeed doesn't do anything unless you switch off fuel pumps from one side. If you did that on the leaking side then you will only end up loosing fuel from non leaking tank. And you did it on the non leaking side the leaking side engine will flame out early. Just follow the check list. Don't device a new one.