Just got a 2005 grey GXP about a month ago (will post pics shortly)... but the small ground effect near the front of the rear tire on the drivers side is loose at the bottom. Does anyone know what I can use to re-affix it? Thanks in advance.

JR, Sorry you didn't get any replies. This is a new one to me.
I looked at mine. Are you talking about the part that'* about 10-12 inches long and runs up between the wheel well and the door? There'* a pin or screw? up near the top, but I couldn't see anything towards the bottom. Sorry.

Yep, that is the piece I am talking about. it appears to be aplastic rivet of some sort and that is fine at the top. The bottom part that fits into the longer piece under the doors coming from the front of the car, that is the part that is loose.

A friend of mine told me to get some 3M double sided tape and try that.

GM used double faced tape and it can separate anywhere front to back on the sides. Mine separated where yours did on both sides, plus the front piece on the back side of the front drivers fender came loose. I had my car custom painted near new and the custom shop used the black urethane adhesive made for body kits when they put it all back together.

I hate tape adhesives. I figure that cleanliness is a little important before applying. Anbody have a cleaner recommendation?

I have used the 3M double sided tape and so far so good. I think tape will be a decent solution here as the pieces fit pretty tight once you get them jammed in there pretty good.

Thanks for your help.

Use rubbing alcohol and then wipe the area down really well with a clean dry cloth. The alcohol will remove the oils and preserver the paint.