I have no USO Products, hence no direct experience....However, it looks like the wall thickness is/was not adequate, took too much meat off when machining. Did you bump the scope ? Even with thin wall, it doesn't usually fracture all by itself. Please post up the outcome, I'm curious.
10/19/17 update; I had no idea that high end scope tubes would be anything other than one continuous, machined piece. Seems like multiple pieces, glued together, just isn't a very good idea. Some scope manufacturers tout the wall thickness of their tubes (in apparent implication of robustness). Then, just to glue multiple pieces together ? eeegads.....