I have had the Nikkor 500 f/5.6 PF lens for about a year and a half I think. I love it, however, for the last couple months the lens hood has become increasingly difficult to get on or off. It just sticks in place when on and I have to twist with all my might to get it off. When I put it on it twists with some difficulty until I get to the final click portion where it locks in place and that is almost impossible to get past. (My 24-70 and 70-200 use the same design and I have no issues with them). Has anyone else who owns the 500 PF lens experienced this?