I've got a similar problem on my 98 Legacy. I've got the stock radio with separate in-dash CD player. The backlight in the LCD display burned out some time ago. I was just at the dealer picking up the parts to replace my timing belt, and asked about the radio. He said that they don't service them, but he could give me an address to send it to, but they charge $120 just to look at it. I think it was manufactured by panasonic.
It seems to me that there should be a way to take it apart and fix it, but without a little advice, I'm a bit leery of trying it on my own. I'm afraid that there isn't actually a light or LED, but rather a luminous LCD screen. If the luminous part of the screen died, you'd have to replace the whole screen, and I'm not sure where you could get the part.
So in answer to your question, I don't know. But if anyone could shed some light on the subject (pun intended), it would be greatly appreciated.