Super Ikonta 530/2 B Speed setting not working. ...

Have removed front amd cleaned lens front and back including front middle lens. Cannot clean back of middle lens due to B shutter speed not working. All other shutter speeds appear to work fine. Remove front name ring, focus prism plate and clean gearing, oiling and greasing for coupled range finder. Every thing appears to work fine. Have begun to remove top plate. All parts needing removeing have been done excepting film winding pin. Seems to be somewhat different from David Richert site repairs. No pin as such. Just a screw which doesn't want to come out before I can remove top. Rangefinder rear sight glass remove. Am at a stand still.
How can I get the shutter to open on the B shutter setting to get to the back of the middle glass. All other shutter speeds, including 1 sec. and rangefinder appears to work properly.
Once top off, how do I proceed to replace the mirror in viewfinder. Inside are appears to need cleaning. Couldn't find instructions on Internet. Any and all help would be greatly appreciated. Anxious to use camera.