Hi Rick,
The first thing I would do is connect an external display to the T5's RGB OUT terminal (aka "VGA" OUT). (Depending on the internal setting, either the internal display is mirrored here, or text/lyrics are always displayed.) Does this still work in your case? If so, you might be able to forego repairing the internal display and work with an external display instead. (You can also find relatively small TFT displays with a VGA input on the Internet.)
By the way, it shouldn't be a problem to still get spare parts for the T5. However, these are not cheap. The original LCD display costs e.g. in Germany around 400 euros and the mainboard (DM circuit board), on which the control of the LDC display is located, over 800 euros.
What I can think of right now: A musician friend of mine had a similar error many years ago (failure of the T5 display). At that time, the reason was an incorrectly routed internal ribbon cable in the display case. It was routed from the factory in such a way that the internal cable connector had come loose after the display had been pulled all the way up (to release the lock and be able to fold the display down again).
I recommend having the T5 checked out by an authorized Yamaha technician. The display case is not easy to open. If you still want to do it yourself (to check if the cable connector in question is properly connected), feel free to contact me via PM for details.
Hope this helps!
Best regards,
Chris