Hi Bernt;
That picture from your manual is essentially identical to the one in my #9 manual. My #9 manual does show the case with the locating finger, but otherwise everything is just alike.
What is still confusing me is in the picture you took of your case, the one where you are holding it between your fingers. There appears to be a piece of metal partially covering the hole in the center of the case. Looks almost like a latch similar to that on a Singer class 15 bobbin case. I have never seen a W&W case with anything there, the case is simply "Trapped" between the holder/drop & hook.
I do have a very early #9 which has the case without the locating finger which should be identical to your #8 case. It has the slot for the thread to pass through beneath the spring though. I have no idea if W&W made some cases of this type when the first added the tension spring to the case or not OR if perhaps this is the wrong case. There were some companies, mostly foreign, who made W&W type machines. Perhaps the case was lost or damaged & someone was able to secure a case from one of these.
I am very sorry I am not able to provide more help, but simply have never encountered a machine before on which the bobbin case did not match the manual description.
Miller/TN
