A caution when purchasing a Hasselblad focusing screen, is to be sure to look carefully at what you are buying, because Hasselblad focusing screens are not labelled with their product number, and are often misidentified. For example, if the focusing screen does not have two notches in the metal border (indicating that it is an Acute-Matte D screen), or does not have a central split prism, it is NOT a Hasselblad 42215. (The reason is that when someone buys a replacement focusing screen, they remove their existing screen from the camera, put the new screen into the camera, and then put the old screen in the box that the new screen came in for storage. Then years later someone finds the old screen and mistakenly sells it using the description on the box. But the 42215 on the box refers to the screen in the camera, not the old focusing screen being stored in the 42215 box.)
Additional notes/comments found on various websites, regarding the fact that modern focusing screens are often made of easy to damage soft plastic:
WARNING: NEVER WET CLEAN Brightscreen or Hasselblad Acute-Matte focusing screens as liquid ruins them. Best way to clean the screen is don't. Even a soft brush will leave scratches. If you must, try a squeeze-bulb blower.
(This warning likely also applies to Maxwell Rolleiflex screens.)
My guess is that a soft brush is not itself the cause of damage, but that hard grit or dust particles on the brush or pushed around on the surface of the focusing screen by the brush is the cause of scratches that are left after ill advised cleaning attempts.
Anyone would be very upset if they ruined a focus screen costing hundreds of dollars to replace. Do any of you have experience with damaging plastic focusing screens by attempting to clean them, or have advice as to how best to clean a plastic focusing screen if it becomes dirty, and is not successfully cleaned using a squeeze-bulb blower?