German lenses not Leica or Zeiss

I have one last 50/1.9 S-K Retina Xenon, actually my first, & still have the import certificate (s/n confirms that). I sold the camera & other lenses. I kept this lens because it's got enough quirks it wouldn't be worth even selling.

The focus is unpleasantly stiff. I will share what I do to get by with it (buy time, as I don't anticipate paying someone to rework it). I don't recommend others do this without considering carefully.

I have access to anhydrous isopropanol...100% isopropyl alcohol, 0% water. I would not recommend, nor use myself, 97%, 91% or 70% because, surely it's obvious getting water inside your lens is undesirable.

I put the straight IPA (don't use beer, either!) into an eyedropper or misting bottle whose spray pattern is predictable and put the smallest amount I can release along the moving helicoid ring, then rotate the helicoid  until it feels like the alcohol has worked its way inside. Sometimes a second or third dose is needed. I hold the lens horizontal unless I feel brave.

When I feel like the helicoid is usable I stop. I haven't had any problems with optics becoming contaminated (yet...but life IS short). After a period of disuse it may or not need a 'booster' infusion, but it's always much better that the initial state that inspired such desperate measures.

I don't know if this is better or worse than the same experiment with lighter fluid/naphtha. Some people clean their shutters with the latter, to the horror of properly-trained camera workers.

Both solvents are relatively benign for such abuse, compared to things you never want to use, like acetone, xylene, etc. Anything that removes paint you shouldn't need further explanation about.

Also be alert for non-metallic components in antique cameras, like shutter or iris/diaphragm/aperture leaves or blades that are made from fiber, hard rubber, gutta percha, etc. Those can swell or warp & not return to proper flatness (ruining mobility).

IPA is pretty weak as a solvent compared to others.

My misguided idea is that the IPA evaporates and I got some more use out of the helicoid.

I will never open another Retina Xenon lens. I didn't have enough hands to reassemble it.