I found this lens at the flea market and thought it would go great on my FTb...until I got home and saw all of the stuff inside the front element. I've seen worse and in fact the rear element is spotless; all of the other elements look good. It's just the front element that doesn't. Is this one worth keeping, in your opinions, or is it trouble in the making? I love the fact that it's a 24/2.8, and I've had quite a bit of luck with Vivitar lenses for the most part. What do you think?