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.
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'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!