This is a known problem and I did a writeup with the part numbers and a few pictures.
No, this is not always covered by warranty. If you have the big warranty (2000 and up) from Isuzu and you are the first owner, then yes you should be able to get it fixed. If you are the second owner or have a 98 or 99, you are out of luck.
Me, I have a 98 Honda Passport so it was up to me.
Here's the writeup:
http://www.planetisuzoo.com/articles.htm/116
Joe