How can I fix this broken cluster mailbox unit (CBU)?
If you know who hit it, buy a new mailbox, and send them the bill. They are liable.

If you don't know who hit it, there's more incentive to save a buck by fixing this one, since most insurance companies will raise your rates if you file for a hit and run, and the raised rates will cost more than just fixing it.

If you can't get the nuts off, either cut them off (if you use a nut-splitter the studs may still be usable) and haul the whole base in to a welder, or have them make a whole new base (the post is pretty thin and may not weld well) and drill holes for new anchors to park it beside the old one.



Put anti-seize on the new nuts - someone will thank you (or your ghost) the next time this happens.