As you've said, it's clear that there is at least one other crack already, and just on that arm in the pic.
I'd also recommend going for a complete new shell, a relatively small outlay off Ebay or similar, and a couple of hours work. If still under guarantee, easier and cheaper still, but you'll lose your AC for a while.
Or you could bodge it up somehow... but that's probably not the best option, IMHO.
No crashes or not, (and I certainly don't disbelieve you), if you are still able to conveniently fire it into dji under guarantee and get it all sorted then it's got to be worthwhile. Winter's coming up, at least where I am, so there are likely to be fewer flying opportunities. Thus it seems like an ideal time to get it all fixed.