: Common in vintage 28mm f/2.8 lenses due to oil leakage. A "quick" fix involves applying a micro-drop of Isopropyl Alcohol (99%) or Naphtha to the blades and cycling the aperture to dissolve the grease.
If you are using the QuickLens Mac App Store tool for measuring and inspecting designs, "fixes" usually involve version updates to maintain compatibility with newer macOS versions. QuickLens 2.8 fix
: Because it is a lightweight tool, most performance issues or crashes are resolved by a clean reinstall from the Mac App Store. : Common in vintage 28mm f/2