Search around on the internet to see if GM has issued any Technical Service Bulletins (TSB) on this particular problem. Considering that they changed the part, it's highly likely that there could be several.
TSBs describe both the problem and the fix for it. Its also documented proof that the problem does exist and GM knows about it. If you can call the zone manager and quote the TSB number and its date, you'll have some solid ammo to fight with.