If this will help at this late date: For years I have been taking apart lenses for issues regarding stiff focus or oil on the aperture blades. It is my assessment that manufacturers overwhelmingly put too much grease on these helicoids. (Nikon seems to be the only one who does not overload with grease.) There are two issues here: the basic helicoid which has rather wide thread-spacings, and the narrow thread which the helicoid fits into. In other words, there are two sets of threads to deal with.
First, with a soft brush and lighter fluid, I thoroughly clean both sets of threads until all grease is eliminated. Then dry thoroughly. I then put, with my finger, a tiny bit of Vaseline (works beautifully, never a problem) onto the threads, making certain not to put too much on those NARROW threads (the cause of stiffness). I put only enough on both thread sets to allow free movement; not enough to migrate to other lens areas and cause trouble. - David Lyga