So did he get new bulbs in there?The previous owner wanted to change them but he broke the headlight "gear" while doing so.
If so, changing the bulbs will obviously not fix it. When I replaced my headlights, I broke the nipple thing on BOTH headlights, but luckily it was when I was done and putting the housings back in. Vice grips should be able to grab whatever is left and let you turn it (it did for me). And every now and then I just push on the headlight lens to make sure it's sitting in there nicely
If he wasn't able to replace the headlights, doing so should solve the flickering problem. Again, vice grips worked for me!