I currently have an Hektor 135 on my bag. No issues and love the lens. mostly use it aroung F/8 so dont really notice soft corners, vignetting or falloff. Will look for a test picture on my files.
Also have the Elmarit 135, but, strange enough, havent use it yet after having it for 1 year. Dont really use that focus length that much and when I need tele, normally grab the Elmarit 90 or the Hektor.