I would perhaps try a Summitar. I've been shying away from Leica LTM lenses because they're more problamatic in regards to haze/fungus and most agree that Japanese LTM's are usually safer in this regard.
The Nikon lens that I own is more than decent for me; I just have this this curiosity in trying out a Leica lens. I will, eventually, just not now unless I get an incredible deal. Leica LTMs still interest me so I may go that route, and from a reputable seller.