Hmm .... is it because the finish on the pen is slightly uneven, making it look like you're trying to see through curved lenses?
You could try making the base part larger, so that the seal cast inside is much closer to the surface of the finished pen. Obviously, this may have issues if someone turns it down just a hair too far and cuts into the seal, but any lensing effect from being under a layer of plastic would be minimal.
Another method would be to ensure than when you create the pen barrel, you turn the section over that seal absolutely flat across the length, so that there is no place that is magnified more by the curvature than any other place.
