Broken viewfinder on Pentax MX?

My friend just picked up her first film camera. It's a Pentax MX and she showed me a weird tint on the viewfinder.
see attached picture. It's not visible when looking through the finder. It mostly only shows when the lens cap is on.
Is that a broken viewfinder?

Looks like either a edge chip of the diopter or starting to separate (if multi-element).

As long as there is nothing loose, sharp or distorting the view, I wouldn't worry about it.

If there are loose glass chips in the camera top, I would stop using it for obvious reasons...

A better close up would help. There may be something going on in the chamber but from this image I at least cannot tell. Are you saying that when you actually look through, as in picture taking, there is nothing out of ordinary?

Looks like partially seperation of a cemented group. Use the finder under utmost extreme conditions as point-light souce in view and check for flare.
Likely you will not be bothered by the fault.

More important: check the eyepiece for misalignment due to mechanical impact. Set the camera strict perpendicular against a subject with an evenly spread structure and check for gradual lack of focus to one side. (Such test would not reveal parallel misplacement of the eyepiece, but such should be rare anyways.)