I managed to find a NOS display for my 640e a few years ago, and decided at the time to drop the LED current right back.
When I had fitted the new display and saw how bright it was, even on the low setting, I realised why the LEDs end up dying.
I can't remember how I did it, think it was just a resistor or two but it shouldn't be too hard to work out.
Drop the current right back so the display is still readable on the high setting.
My set has been running with no lost segments now for a couple of years.
Uniden here told me at the time that the display module is obsolete - no longer made, and that they had no stocks of them even in Japan. I managed to get their last one.