My friend has an 03 sl500 and the right front low beam quit working.I don't think it's the bulb,possibly the ballast or the ignitor,does anyone know how to check them before spending a fortune? He had it checked at a local nonMB dealer and they told him it was the ignitor and would cost about $600.Want to be sure that is the problem,that price seeemed a little pricey to me.TIA