It can be done, mine had gone. You actually have to buy tiny bulbs with exposed wires and install it. I took photos of it but did not post as i wasn't sure. Anyway... you need to take the radio out first and pop off the panels underneath to make it easier. I will try to relocate my photos, if I find I will post direct or load here.
I just popped into my shed and located the packet of bulbs I bought I have 2 packets that are possible but I am sure it is the smaller bulb, called T1, mine are 12v 60mA (RS stock 587-670). I forgot whether I had to solder the flying leads to PCB or just trap them in there holder.
Going to look for pictures......