Try this:
Key in 12 8's.
Turn the contrast all the way up by holding down the C key and + key at the same time.
When it stops increasing in darkness, hold the calculator so you can change the viewing angle of the display.
Angle the display so everything appears darkest, especially the annunciators.
Is the right side of the display the same contrast as the left?
If the left/right sides are different, it may be one of two different problems:
Missing pieces of digits or annunciator: loose connections between the circuit board and the LCD (easy repair)
or
The right side seems to fade away to nothing: a bad LCD (still repairable, but hard to find a spare LCD).
IMHO, an eBay price in good condition would be would $40-50 and up. All depends. Have the manual? Add $15-20. Start the bidding at $10, no reserve, with a 7 day auction and the market will determine what it's worth. Even with a broken LCD, it's worth something since the logic board works. Don't toss it!
Please let us know what you find with the test.