It might be helpful to see some of the actual not flat and level. Could you take a picture of the view through an eyepiece?
You can use a camera with a shallow lens and a small image sensor, a cellphone's will probably do, and hold it above the eyepiece. If you hold it perpendicular, centered and near, then slowly pull it away, you will see a bright spot as the projected image enters the camera's focal plane, that quickly dims a bit as the camera adjusts the exposure. If you move the camera away and toward the eyepiece, you should be able to see the eyepiece's full field of view, side to side(*). Try for somewhat dimmed with a sharp circular edge. Then you gently take an exposure, trying not to twist or move the camera. I can lightly press against the eyepiece to steady my hand.
It takes a little practice and a few tries, but it can be handy skill.
I have attached a picture I just took through the eyepiece of an American Optical 40, student microscope, with an old 2 megapixel
Sony U30 camera. (It is a good camera, but a more challenging microscope, for this.) It is the best of eight, from two sets of four. The first set did not have enough light; the second are a little rotated because the sun was washing out the old technology view screen.
(*) EDIT: You may get some cropping (letter boxing) at the top and bottom. Try to make it equal which will help align the camera over the eyepiece. [I need to get some more sleep.]