I would leave it unless it gets worse. Most of the plasticky zoom Nikkors of late are like this, including the 24-85 G, and all the 18-xx DX zooms. They break easily, but as long as you pamper them, they'll be okay. The 28-105 is better than most, though. It is a lens I use very often, and I have a high regard for its overall performance. If yours eventually moves into the Great Circle of Confusion, so to speak, then a replacement should be around $200, which is a lot less than the lens is worth in actual use.