Originally Posted by summicron1
if there's a retaining ring in front of it, try screwing it down using only finger friction so you don't scratch the lens with a screw driver or something.
if not, send for repair or find another lens. They can't be expensive...
It's not the retaining ring, but the whole of last end section of the lens. I guess it holds the last element.
They can't be expensive
Leica lenses? They are expensive enough.