Originally Posted by IIIg
Your chances of finding a useable J8 are quite a bit better than a useable J3.
Quality control on the J3's was evidently poor. Many of them require shimming to focus properly on a Barnack Leica.
My own experience with ten J8's (then used to be inexpensive) was that they were all useable when they reached me (silver and black bodies both). Only one of four J3's was anywhere near good focus. All of the bad J3's were quite sharp lenses after having been shimmed properly.
You have odd description of bad and quality control. Sounds like total newbie in RF.