My understanding is no GM vehicle came from the factory with undercoat. It was a product sold and installed by the dealer as an add-on. Most did more harm than good because the person applying it would usually spray over and plug the drain holes causing more rust since any water couldn't drain away.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.