I'd reccomend replacing the bulb. this is not a complex project... pay close attention when you remove the existing wiring, and install the new bulb exactly as the old one was wired. You may need to drill of shim a little to make the new bulb fit, but it's a chance for a good education in wiring, with very little risk. Worst that can happen is you have to replace the whole thing anyway.
This kind of stuff is what I think is the fun part!
Well if I were you I would replace them, but if you don't want to replace them I have a site that could help you. Now I can't put the address on here but go to Google and then click images then type model traffic lights and click the first top left hand picture.
I think you'd be better off replacing the entire unit, considering how they are made and their cost.
Add a resistor with a value of 10-20 Ohms to the new unit's power connection and the bulbs will last much longer.