I had a 99 F53 V10 and 2 on the rear passenger side were broken and gone. When I went to remove the manifold 3 more broke off as soon as I tried pulling them. I fixed the passenger side by replacing all the studs in a SnowBird Park in AZ then drove it home and yanked the entire OEM exhaust and replaced it with a Banks system.
I now have a 2004 E450 at 32,000 miles and I am expecting the same BECAUSE we winter drive on salt roads to and from AZ twice a year.
Sorry, I know this rant does not help you other then to say "you are not alone".
