I have a Vitomatic II. This has a meter, but it is read from the top. It's not visible in the viewfinder like the IIa, so I don't know how the IIa viewfinder is arranged optically to show the meter.
When I got this camera the rangefinder image was virtually invisible due to cloudiness on the movable lens behind the rangefinder window, caused by droplets of liquid (possibly from evaporation of lubricant?). This lens is not within the optical block, but it is not easily accessible without some fairly scary-looking dismantling of the rangefinder. I managed to get it clean by sliding in small pads of tissue with a little naphtha from the side.
Have a look from the front through the rangefinder window, Jurgen. If it looks cloudy, maybe you have the same problem.
Steve.