The black-out version is a lost cause.
The flickering dim one MIGHT be rejuvenated by taking it apart - carefully.
As you remove the glass, there is a foam "zebra connector" that brings power to the circuit on the glass. The zebra connector has strips of conductive carbon embedded in the foam and non-conductive strips. That way, when the foam block is properly placed, the circuits on the glass are properly fed from the PCB. Take it apart, hope the glass is fairly clean, clean the circuit board with clean water and soft Q-Tips or cotton balls or wood tongue depressor sticks/toothpicks. Make sure you do not scrape so hard that you pry the copper from the circuitboard substrate. Gently wipe each side of the zebra connector with distilled water. Clean the glass display with distilled water (where the zebra connector touches the glass).
Let everything dry well (overnight) and then reassemble.
Good luck. When you open it up, there may be big patches of green copper corroded PCB oxidation. Try not to rub this off too much. The little bit of copper metal may be barely holding on to complete the circuit. Be delicate and remember that crud/corrosion with an electrical connection is better than perfection on cleanliness with broken connections.
If the black bezel is ruined, you can use your artistic ability to make a new one with PowerPoint and a nice printer. I just used paper and a black/White laser printer.
It is usually a spill of NaOH or other caustic powders or liquids that cause this in chemical labs. I've cleaned a few in my days in the lab. They usually work and I had no experience the first time I cleaned one.
The good news is that you don't need a Sartorius balance to be successful in the lab. Those used to cost $600 to several thousand dollars 25-years ago. Cheap, Chinese-made balances are now available for under $100 and some one-decimal balances can be bought for even less ($20) on Amazon or eBay.