I'm not very familiar with the workings of a G5, but I'm going to assume it has an intake manifold made up of some sort of composit matieral other than aluminum or steel. If so, these can warp and cause an antifreez leak.
I'm not sure if a simple gasket change will fix it or not.
Do you notice the fluid level rising on your oils dipstick?
Do you see any tracks of oil running down the side of the motor, and dripping on the floor?
When the motor gets warm, can you smell the faint sweet odor of antifreez being cooked under your hood, or from your exhaust? See any unusual smoke coming out of your talipipe?
Every symptom I mentioned usually has a different cause.
Try to pinpoint exactly where it's coming from, and where it's going. (Something Mr. Goodrench should be doing).
Causes can range from warped intake manifold, bad gasket, cracked cylinder head, and the list goes on.
Since you've reported the problem right from the start, and it seems as though it's been an on going problem, there should be a history set that would require them to continue dealing with it even after your warranty is up. Good Luck