Went in for oil change today and asked them to replace my bulbs which I purchased from RockAuto. Unfortunately they weren't able to change the bad side (passenger side) because they were unable to pull the bulb out. They think the passenger side bulb melted so they asked me to find the part which the bulb connects into. They didn't have a part name or part number for me. Apparently it's called a "Ballast" or something but a quick search on RockAuto returns no results. Can anyone here help??? Where do I buy this replacement part? Is it expensive?

FYI Driver side came out with ease, but passenger side was stuck on hard. The bulb they pulled from the driver side was labelled KOITO JAPAN 35W D2S DOT...quick Google search shows they use to come OEM with some older G35s so I assume these bulbs shouldn't be cheap enough to be defective like that??