Aperture ring good in one direction, tight in the other -- why?

I just purchased what appeared to be -- and is, for the most part -- a good condition 50+-year-old Nippon Kogaku 5cm f/2 NAI lens, as supplied with some of the first Nikon F cameras. Nice lens, my second copy. The only odd thing about this lens is that the aperture ring turns easily when moving from f/2 toward f/16, but it's quite still moving from f/16 back to f/2. The blades are snappy at any f/stop.

Now, I'm not surprised that an aperture ring would be stiff, but in my experience, when it's stiff, it's stiff in both directions.

Any thoughts on what would cause the asymmetry?

Perhaps I can open the lens myself and have a look, or I may send to a repair shop for a re-lube, as I presume that's what the root cause is. If anyone can suggest a good shop for Nikon lens re-lube, I'd appreciate a tip. I also have an f/2.8 macro-Nikkor that needs work for a very stiff focus -- in both directions.

It's only a couple of screws holding the mount on. When that's off the aperture ring should slide off.
There MAY be a ball bearing for the click stop.
Since the aperture works OK The ring's binding. Why? If the lens has been worked on the original bearing may have been lost and replaced with a smaller one. Or the bearing's gone and the spring behind the bearing is causing the bind.

Why would a smaller bearing cause stiffness in one direction only?

Thanks

pentaxuser

Sounds like it is time for a CLA.