I know that these cars have issues with the fog lights buring out, but in 6 years I've never had to replace one yet. I had to replace both back-up lamps, but that was a 15 minute job that cost $4.97. I have really been blessed with a goodone with literally no problems, so I can't complain at all. GM made a great midification to the Nothstar in 2004 adding cylinder sleaves and coating to the rings. This eliminated all that loud piston clap when it was cold. As for oil, I've always run full synthetic in mine with a Fram Extra Guard filter. If you maintain the Northstar....it will take care of you.

GREAT FEEDBACK everyone. This forum is awesome. I hope GXP VENOM posts a response with a little more insight to the motor/smoke question and what it is. I will check out the Cadilac/northstar forum too for more info.

i had the GXP for a very short time in stock lighting, but when i got the car both fog lights were fine, and i installed HIDs and they are flawless for 2 years now.
they say "The GXP was more of a hit and miss" but i dont believe that, i think it all depends on how the pervious own took care of it, when i bought mine it was a lease return by some guy in a city close to mine, the back seat was never sat in, and the front was flawless with less than 25k miles on it. i take care of it really good, and so far its amazing
I also think a big part of the issue is when they go into service for minor things, most GM service men dont know how to take a GXP apart and put it back together, many times GM itself will ruin your car, this just happened to me this month, 6 times into GM in one month because of something they screwed up

as for the smoke, why dont you ask the current owner about it or ask them to check it and let you know since you're serious about the car