UV exposure can degrade paddle shaft materials, so I don't blame Werner
for not covering this under warranty. The good news is that it can be
repaired.

There are several ways to address this problem. The first thing you need
to do is to lightly wet sand the shaft with 400 grit wet/dry sandpaper
to remove any loose fibers. Once you've done that, you can either apply
the shink material that Werner provides or you can coat the shaft with
something. You could just use paddle or surfboard wax as was suggested
elsewhere, but since the resin matrix is already degraded, it would
probably be wise to protect it more than wax can. You can buy spray
clearcoat if you like the original color or you can paint it if you want
a new look.