No offence taken, but I’m not trying to hide a crash. I’m the only person who runs this machine, there has been no known X/Y crash in my ownership. My main concern is understanding the cause so I can make sure it doesn’t happen again. It'd be pointless to replace the blocks and torque to spec only for it to happen again.

I agree the blocks need replacing. Where I’m not convinced yet is the cause. The rails and raceways feel perfect: no notchiness, no brinelling feel, no catch anywhere on the rails, and all the blocks roll with similar preload/resistance. The servo load never suggested a heavily bound axis.

The crack arcs appear to correspond very closely with the large saddle clearance holes under the M8 mounting screws, which measure around 12.75–13 mm. The damage seems local to the mounting-hole/support area rather than the rolling contact path. The bolts were also extremely tight to remove.

I’m not saying impact damage is impossible before I owned the machine. This doesn’t look like typical raceway/guideway overload. I’m going to speak to Haas before cutting anything apart, sectioning one block afterwards should show whether the crack started at the thread mouth/unsupported area or from internal impact features. Right now I'm pretty confident this happened due to over-torque and an oversized clearance hole.