I've been using the Pentacon 50mm f1.8 with pleasure on my Canon 550D with the help of a M42 to EOS adapter.
Some weeks ago however the lens housing got damaged in my luggage such that turning the focus ring became difficult. After I applied some torque on the focussing ring (by hand, no tools used) the lens unscrewed. The lens now consists of two parts as shown below.
Screwing it back together seemed easy, but it proves to be quite hard. I have to align some notches and the aperture control lever before it can be screwed together. I've tried it now for a while, but either the notch doesn't align or the lever doesn't fit.
Is there some kind of trick in doing this? The lens cost me €10, so going to a repair shop is not worth it.