It's sad that these cars are such freaking rust buckets. When I see one in a junkyard here in NY, I'm always shocked at how bad the rust is. The whole underside of the car is gone. Other cars of similar vintage (or older) aren't event close. I haven't had any issues with bolts yet, but snapping off screw heads on parts under the car is getting common. Fortunately, my daughter's P5 is a southern PA car that hasn't been subjected to a NY winter yet (hopefully, it never will). It has a couple of spots that have needed attention, but it's pretty clean for a northern car. The first thing I did was clean and treat any spots, then undercoated/rustproofed the entire car. That'll slow it down a bit.