John, that damage is pure bad technique in trying to get a stuck chuck off. The metric spindle was about .0010” more than the aftermarket chucks sold in the USA. Grizzly chucks fit from the get go, but that information was not passed on by Grizzly, as I suppose their thinking was it matched with their chucks. I have seen a lot of tolerences all over the place on different chuck inserts....even from the same manufacturer. I had genuine teknatool inserts that had different measurements. I think they probably came from different runs at the manufacturer, as some were purchased 3 or 4 years later than others in my chuck collection.
I remember one turner [Fred in WVa.] who broke the spindle housing on his G0698 18/47 back a few years ago, much like the G0766 you have pictured above. The G0766 is a very good lathe, but those metric machining specs did cause a few problems along the way for some who did not take the time to read up on postings from experienced users. As I mentioned earlier, Grizzly has changed most of those specs along with new orders of the G0766, as they had returns and figured out things....customer feedback can really give them an education!
The G0800 is much beefier in the castingss, and has a totally different spindle lock design, and is a higher class of lathe, really comparable to the PM 4224b, but with ergonomic design elements the PM does not have. The banjo is beefier than the banjo on the Powermatic or the Robust American Beauty, tailstock is heavy, and everthing locks down absolutely rock solid. A really fine lathe.
Remember, in a moments time, everything can change!
Vision - not just seeing what is, but seeing what can be!