Fix this yourself.
Either the transistor is bad, or the logic chip driving that transistor is bad, and that line is stuck high, causing the transistor to be stuck on.
Those transistors/lights are not intended to stay on continuously. They're meant to have some duty cycle, where they are flashed on and off. So that's probably why the transistor is darker than the others, it's just gotten very hot because it's stuck on.
A similar thing happens on Sea Wolf boards. If the game board locks up, a bunch of the lights get stuck on, and it blows the transistors that drive them. In that case the transistors are so small they can't handle being stuck on at all, and they melt in a few seconds. On that RD board, it looks like they are using beefier ones, that maybe can handle a continuous duty cycle. But they are still going to get pretty hot.)
I'd replace the transistor first. And if that doesn't fix it, replace the HCT175. (Or you could replace the 175 first, either way.) You might be able to test the transistor with power off, and compare it to the adjacent ones, to see if it's bad, before replacing anything.
You'll need desoldering tools. If you don't have any, now is a good time to invest in some, and learn. Replacing those two parts is relatively easy, and will save you from having to deal with returning the board.