The LG Expression on AT&T looks the same as my LG Rumor Reflex, except the color is different and there is no mirror on the back. The software is different too.
Broken Phones Kyocera Torino on Metro PCS- Does not turn On. iPhone XR- Works, but it is FMI On, beat up, and iCloud Locked LG Rumor Touch on Sprint- Broken Screen, but works Samsung Sway on Verizon- Broken Screen, but works BlackBerry Curve 8330 on Sprint- Broken Trackball, but works BlackBerry Curve 8330 on Verizon- Broken Keyboard, but works BlackBerry Storm 9530 on Verizon- Bad Software, but works
perhaps you can cannibalize your stash of broken/unfixable phones to replace the scree of the LG 505C. my opinion about the yellowing of the screen is that it is dying. i had the same issue with my generic android screen years ago.