Gotta love plastic - NOT!
One might thing that the trillions of coolant elbows on Buick V-6s which failed for a decade before your Yukon was built would have been enough of a lesson for GM, but alas, the accountants and 90-day wonders apparently won out over the engineers once more.
Glad you got it home intact, but if it continues, your roommate might decide to take the horse and leave the trailer and Yukon at home next time.
I'm guessing there may be some sort of permanent "fix" for the plastic, even if home-grown.