There are a few oil points that easy to overlook in this area, and it will make things turn sluggish. Archaic Arane has
a good post on them. Make sure all movments, jont, gears, hinges, etc, from cam stack gears to swing arm move, poke at springed parts like the swing arm (needle bar) to inspect. Get oil all the way down to the gear under there too.
Can you compare to your other 401?