I am posting this for information. I have a 99 F-350 CC ESOF 4x4 with 25k miles on it. I am in the process of trying to get Fo Mo Co to buy this truck back as it has been a let down from the day I picked it up.
It has been in the shop 15 times with many different problems but that isn't important. What is important is that the dealer had to rebuild the internals on the transfer case because they were "disintegrating" as they put it.
This was the reason they gave me why the truck rolled backwards, down a hill, while in park, after I got out of it.
After it was rebuilt completely, the manufacturer of the transfer case (New Venture) asked for the transfer case back in exchange for a brand new one.
Personally I doubt this is an isolated case. I have read of others with bent shift forks and problems with transfer case internals.
It also took a year to get the problem fixed because the shop foreman was convinced the problem was the transmission and not with the transfer case. It took another dealer to find the problem.
Sorry for the long post but I just want to give everyone a heads up on a possible problem.