Bad backlight - chances it's the screen not the main board?

Hi everyone, got a water damaged phone on my hands! Any advice would be awesome! The top backlight still works - as a matter of fact I'm typing this on it! Problem is the main bottom backlight isn't functioning, so it's impossible to use in day light. When the phone was submerged it was powered off. I cleaned the main board with isopropyl, but obviously there was quite a large amount of water underneath the screen that never seemed to dissipate until two weeks. Mainboard doesn't appear to have any serious stand out issues from visual inspection and everything else works fine. So my main question is for all the experienced cell phone repair people out there... How often are backlight issues just the screen itself? There's quite a bit of electronics on the back of it let alone the LEDs. It seems to me from reading that it rarely is, and is probably the main board's fault. The reason I ask is because I can find LG v20 screens with the midframe online for around C$100, but the return policy states unless its defective I can't return it. Should I just do it anyways and return it if doesn't work? I phoned all the cell phone repair shops in my city and none of them carry extra screens, but they can order one and if it works charge $250+ for something so trivial. Is it worth trying? Or is it almost gaurenteed to be the main board? Thanks everyone