I just installed a curt hitch receiver for my 2017 outlander. I'm having trouble with one bolt (per side). I have all four that bolt on horizontally but can't get the two that mount vertically into the frame. It's a factory hole that's supposed to be threaded I've use a small wire brush, lots of spray oil, even a tap to clean the threads but unable to get any thread started. Anyone have experience with this factory hole? Only thing I can think of is maybe the supplied bolts are fine thread and the hole is course threads?