[f5fstop]

Not sure how the coolant stains, or if it even stains. What surprised me is the cracked heater core. We were just discussing this at work the other day, making comments about what a pain the arse it is to replace a heater core on most modern vehicles (remove entire dash on most vehicles), and one guy pulls up warranty stats and heater cores were not even on the list.
From what you describe, it appears a bad one slipped through the manufacturer's quality control. If it did stain, the dealer should replace the carpeting, if it didn't stain, no stain will appear later. As for scotchguard, don't believe scotchguard is applied to the carpeting.