The tips do eventually wear out...especially if you use it a lot.

Have you tried contacting Weller about it?

If you replace the tip, I've heard that you should turn the temperature down (you have one of the neat adjustable temp irons, I assume?)when you're not using the iron so that it doesn't damage it, if you decide to keep it warm for instant use on the bench.

Here is Weller's website. They are now a part of Cooper tools (the same people that bought out the venerable Eagle Electric [Linked Image] ).
http://www.cooperhandtools.com/brands/weller/consumer_soldering.htm