This instrument was dropped either during shipping, or other handling. I have worked on many dozens of 576's, and have seen this before. The CRT impacted the top of the frame. The face plate has a chip out of it, but should not leak, just be careful with it!
As for the collector supply isolated chassis, the same thing happened. An impact broke the insulators. Unfortunately, Tek used the same plastic for those, as for their knobs, an unfilled, weak styrenic, that breaks easily if placed in tension.
These two chassis must remain electrically isolated, to about 2KV. The floating top half, if it moves too much, will break the coupling on the Looping control, and the Polarity switch coupling may disconnect. These are difficult to repair..
Good luck with your 576, a truly great instrument!