Santino
Even a Contax II will have frame spacing problems, the fix is simple but dont do it unless you have >1mm overlap or torn sprocket holes.
You are cleaning a slipping clutch like on stick shift auto.
You need a screw driver to fit the three screws holding the take up spool in place. Remiove three screws over a deep tray, steal a coffee tray from houshold. Stick the screws to sticky tape.
There is a screw in centre of take up fork, need a screw driver to fit this accurately. Remove this screw with the camera upside down, counter hold the fork (shaft) with pliers, protect the shaft with rubber gloves. You need to make a record of the sequence of the washers there will be one or more under the screw and one or more the other side of the fork, and a spring.
Clean each part in Zippo fluid or alcohol with cotton cloth, reassemble in same (reverse) order, use the rubber gloves as glooves for Zippo.
To test the camera is ok you need a scrap film and a (soft graphite) pencil, load the film normally, remove the lens and shoot each frame on B, marking the film through the shutter gate. Remove the film and look at the separation.
Right don't do this unless you have torn perfs or >1mm overlap, it could make things worse. If this does not work it is add a shim or compress the spring...
Varjag
My FSU collasibles and old Elmar are like that, and some other more expensive, washed out colours and iris images but my J8 and 103 are ok. I do use a deep hood on all my shots. One of my j12 does seem to have a hot spot problem, but it may have had a filter on it.
I wont strip a lens without cause and my 103 apart from being homely and looking like it needs more paint is ok, I'll have to try it again.
Are you sure your 103 is clean (inside) have you projected a torch light (flashlight/lamp whatever) through it, in darkened room?
My standard test is low sun in picture, varies with cloud etc., but hood does not help.
Noel