Its not common, but not unheard of either. There is a gel like liquid that suspends the fiber optic in the protective housing. We've had several reports of that gel leaking out. Its not dangerous, and in fact, by all accounts, doesnt even effect the function of the scope in any way. However, if you'd like, Trijicon will fix this for you. It will require you sending it back to them, and maybe a couple weeks, but you'll get it back with a new fiber optic and wont be charged anything.