I’ve dedicated a large portion of this article to explaining why sending a camera to the shop isn’t always feasible. I’ve also cautioned the reader against forcing any components into movement. I’ve since added edits to clarify those points.
That said, slow shutter speeds can have various causes, including oil vapour on the blades (which is addressed in another portion of the article, analog.cafe/r/home-film-ca…) and various kinds of oil contamination. Proper re-lubrication may solve these problems, but this procedure is costly, and it comes with additional risks of wear and, as you said, improper lubrication.
I reached the above conclusions based on my experience and extensive research. Following your concerns, I’ve asked around and received similar responses (like this mas.to/@sandehalynch@masto… and this bsky.app/profile/an.empty.…) from people who repaired numerous shutters, including the brands you mentioned.
Dmitri