On another note, is there any impact damage on the camera, namely on the rewind side of the camera, near the prism? It may not be a lubrication issue, but impact damage that's causing the coupling ring from returning to rest. My F3P has a similar problem, but it now only occurs if the ring is moved all the way to the f/45 position. That's due to the impact damage that was caused by the previous owner dropping it. Also has a loose PC socket and a dead F3-specific hot shoe. Also seems to have affected the shutter speeds above 1/60.
Previously, it was also slow, and the service tech used some Hexane to clean the ring, then reassembled it. Got rid of the slow response, but the ring still hangs as mentioned above. Luckily, no AI/AIS Nikkor has f/45 as a setting on the aperture ring.