Bill, the framecounter assembly is very simple on these and common between the Ikonta 35, Contina (with or without uncoupled rangefinder) and Contessa. There is one major "gotcha". The rewind button is threaded but I have now seen a few where the post it threads onto snaps off when its overtightened. So be gentle with that or you won't have a rewind button! I can't say how much force it takes because I haven't broken one but take care. I had an Ikonta 35 where I used a paper slip shoved into the hole to push the cassette side release in. Not convenient but useable.
Zeissfan, its in my pocket most days but its one of those darned long rolls of 36 exposures of slides! Its in my jacket pocket now and just about done. I like 12 exposure 120 better for this reason!
Did Herr Nerwin not also design the Contax II, III, IIA, IIIA? (he left before the colour dial models came out)