Screen has gone dim on right side

I don't know this device, but calculators and similar devices with monochrome LCD displays often use the same method for making the connections between the circuit board and the LCD. The LCD is glass so obviously you can't solder to it. The connections consist of thin, barely visible conducting tracks deposited onto the glass, and these need to be connected to pads on the circuit board, which are laid out in the same pattern (in a row) and the same size.

A strip of rubber is placed between the pads on the LCD and the circuit board, the strip having lots of separate conducting tracks around its circumference, allowing it to conduct in a direction perpendicular to its length (i.e. between the LCD and the circuit board) but not along its length (which would short out one pad to the next). It depends on there being sufficient pressure on the rubber, both from the circuit board and the LCD, in order to make good contact.

After a while the rubber can become tired and no longer makes good contact, and I suspect that's what might be happening towards the right hand side. If you can reseat it and maybe somehow increase the pressure, maybe squeezing it in a direction perpendicular to the current flow between the LCD and the board, you may be able to improve it. Alternatively, those rubber strips must be a commodity item, but I've never found a source (not that I've tried very hard).