I just finished repairing this Jena 180mm 2.8 in a Hasselblad thread mount. What a challenge! The lens retaining rings each were frozen as was the secondary helicoid. When I got the lens it would not budge. The aperture would work fine but the focus was locked. The culprit was the secondary helicoid (very fine threads) but getting to it and freeing it prior to cleaning proved to be a bear. The old lubricants had turned into the equivalent of “thread locking compound”. I thought the threads would be damaged from constantly moving the rings clockwise and counter clockwise over and over and over again. But interestingly there was no damage to the threads each time I removed a ring other than some scratches to one ring, not the threads, when the lens wrench gave way. It took hours and hours to get this right and the only thing that worked was heat. Orsetto knows from a previous conversation that this has worked for me in the past. Don't underestimate the power of a hair dryer, welding gloves (the metal gets too hot to hold) and some naptha. I didn't have to resort to using the barbeque grill this time as I had to with a Contarex 135mm. This was a labor of love because it would be cost prohibitive for a tech to spend as much time as I had to. The end result is a dust free optics package and smooth focusing once again. I’m looking forward to a dry day so I can start using this “Bokeh Bomber” (18 aperture blades!). Here is a shot of it on my 1000f.