Ok. So this one has shutter speeds all messed up. There is an orderly method depending on speeds above the X synch speed or below.
Above X-synch the speeds are controlled by curtain timing which varies slit width. Below X synch the escapement times the shutter. The escapement; usually 3 or 4 steps both with and without the pallet (which slows it considerably) giving a total of 6 to 8 slow speeds.
I recently acquired a well-used F + lens at a local camera show. The shutter clearly operated, but on a brief test of it, 1/8 and 1/15 were really slow, like 3 stops slow. 1-1/4 were fine and the faster speeds were decent. Yes, that meant that 1/8 and 1/15 were slower than 1/4. I think that 1/8 and 1/15 are governed by a slightly different mechanism of the slow speed governor (I think that's what you refer to about engaging the pallet or not). I opened up the bottom cover of the body and it didn't seem dirty (I don't think you can really see the slow speed governor from there), so I blew on it, gave it a stern glare, and closed it back up. After exercising the shutter through many speeds and firings, the 1/8 and 1/15 are almost up to speed. The rest of the speeds are within 1/3 stop.
OTOH, my first F that I've had since 1985 - so it hasn't been abused, or serviced, for several decades - has speeds that are dead-on today using a photoplug-type tester. I got it because I wanted a reliable SLR after my first one broke. Unlike a lot of things I do, that worked out.