Depending how careful you are and whether you have no qualms with doing this, there's temporarily "borrowing" another n2DSXL to swap motherboards so you can ntrboot re-hack your mobo, backup everything, swap back the mobos, and return the store purchased n2DSXL, like the techniques noted below.
I would seriously consider selling off your broken n2DSXL for parts, buying a n3DSXL, and transferring everything to that if build durability and repair-ability are big concerns for you.
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Another option is to send it in to get repair by 3ds repair specialist wiigotem.
Just let him know what's wrong with it on top needing to rehack with ntrboot / CFW.
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Very tiny pin hole scratches from the farthest end points along each of the traces if there are no exposed contacts. This is if you can't visually verify there are breaks in the flex cable, but you have a strong suspicion it's coming from that cable.
This does have the drawback where doing this can break the traces, and you would have to patch the exposed layers with tiny strips of tape. Delicate hardware repair is often a messy affair.