Engine cover has been off for about 8 years. My car never gets driven in the winter or even if a hit of salt on the road in the spring. Never gets driven in the rain and is always parked in a garage. When the car is washed it is always driven afterward until the engine is completely warmed up and then it is parked with the hood up in the garage to dry things out. I hope these things help eliminate the potential problem the OP mentioned.

It would be interesting to know if the cars with damaged bolts were ever driven in the winter.

 

I cut a big sheet of heavy duty plastic drop cloth that covers the engine completely and put that under the hood when washing.

 

Early on in ownership ( v6 manual trans) I was fortunate to get a pair of the Jaguar black with chrome trim hood vents. These were to replace the open mesh ones that came on the car, OE I'm assuming. At first I was concerned about increased trapped heat, but later I realized these replacements shielded the susceptible engine areas much better. They do have an open area, but not as much as the mesh version. Car has been driven in the rain, and at least once torrential. Garaged to allow drying out. I had the flanged heater pipes all replaced, as well as SC oil, so hoping nothing has corroded since then.