Locking hubs are like any other part of the truck, if you don't maintain them they will start having problems. I had a set of Warn premiums for around a year or so when they started getting a little "sticky" when locking them in. The splines and such are a pretty tight fit together, so it doesn't take much grit or rust at all to cause problems. After taking them apart, cleaning them, and applying a real light coat of grease they again work really smooth. I found that some light spray grease works really well and doesn't require the hub to be completely take apart.
You have to remember that it's pretty common to get at least small amounts of dirt and water into the hub. The dirt and rust will buildup and can cause some problems, and you can also get condensation inside the hubs when running warm parts through cold water holes.
I have never had any fitment problems with the Warns.
