You can tell quite a lot about the spindle by checking the quill stays put laterally when you load it by setting up a DTI against it, yanking on the chuck sideways. The chattering could be the spindle, but could also be something amiss in the chuck. If you can eliminate the chuck as a thing to blame, it might help. A bent spindle lets you know it's in trouble, even when not under load.
The key thing you mention is it "had a bad crash", and that the chatter condition has been present since that event. It is reasonable to infer that there are things in the load path that are now either damaged, or not as they should be. Have a look at the pulleys when turned by hand, with the belts removed. A sudden stoppage can do things to them! Let us hope there is no crack in the frame structure up to the pole support. Check the condition of the belt(s) to discover if they have come out a bit "modified" after the event.
I have a (new) drill press that is still a mess of unwanted vibration and noise. The cause happens to be out of balance pulleys, but the noise is not the moan nor high frequency shriek I would call "real chatter". That would be the kind arising from lack of rigidity in the load path (like a frame crack or suchlike).
Maybe a picture or two of the stuff you think might have taken most of the hit during the bad crash would help. I'm betting there are folk here who have experienced your scenario, and perhaps much worse!
