Headlight problem

Sams370z

So a couple months ago when I first bought my 370, I noticed that my driver side headlight was out. I called the dealership and they told me 2 things; 1. they couldnt fix it since they werent a strictly nissan dealer, and 2. that the headlights werent covered by the warranty anyway. So i take it to a nissan dealer and they tell me the balast (not sure on the spelling) was out and it needed a new one. So $XXX.xx later, it is "fixed." After a couple night drives I have discovered that my "fixed" headlight shuts off after being on for 10 seconds, and that it will only stay on if i switch them off and back on again. Plus with the lights set on automatic, every little bump shuts it off again. Anybody else have this problem, or is it something that I should bring to the dealer as a possible fix or trade?