So, yeah, that section of undercoating just came off the face of the cross member in one big piece. We were floored! (I like puns) So, we decided to just remove ALL of their stuff and recoat the entire bottom section to insure a consistent robust barrier against corrosion. As we went along, it became clear that the affected area was limited to that one area, but we had already started and are sticklers for detail, so we forged on. Let me tell you, it was no easy work. It took a couple months just to do that, with us working on it only on the weekends. Scrapers, wire brushes, wire WHEELS, steel wool, acetone, etc. all came into play. I really wish they had applied their undercoating properly everywhere.
As it is now, all of their undercoating is removed and the whole bottom section is primed. I still have to spray the actual undercoating.