I've noticed little pockets at the front of the shuttle travel with felt in them on several of my machines. In the wall from the pocket to the shuttle is a small hole. Those are to be filled with oil so the shuttle doesn't ride dry on the machine.
I've removed the old decayed stuff in the pockets, cleaned them and the horizontal hole and put in new felt. Then each time I use my machines I fill the pocket with oil.
That actually made a noticeable difference in how a couple of them sounded. It can't do anything but help the machine.

For the machines that do not have the oil pocket I put a drop of oil on the arched wall of the machine every time I put in a new bobbin.

Joe

Problem solved, Operator error!
 

Distracted myself by looking at a symptom when the real problem was further upstream!
I even carefully compared it to the stitching of my Windsor B, to see what the WB was doing that the NH wasn't.
Here are some symptom closeups...

see the loop forming topside...
[ATTACH=CONFIG]459933[/ATTACH]
[ATTACH=CONFIG]459934[/ATTACH]
So the needle would occasionally pierce the loop, and break the thread... and the problem was actually...the take up lever wasn't moving. Because when I reassembled the needle bar assy, I neglected to re-engage it. Duhh. And now it's better, much better. Now I need to get a little more traction out of the drive wheel, but that's easier.
I'll post a photo of the culprit, once I get my Netbook to let loose of the SD card so I can put it back in the camera. Sometimes problems are simpler than we think. Good news is, I now have 2 extra shuttles, (new) because the old one is working fine. Oh, I did squeeze down some of the free play around the shuttle, thinking it might have been that, and had to back it back out a hair. I love puzzles!

Awesome! Success feels so good...

Take up lever, spring, do-hickey
 

I think this one may have actually been fashioned by someone other than the factory.[ATTACH=CONFIG]459953[/ATTACH]
Lastly (I think) on this one, I need to figure out what gives with the overcenter spring on the plunger of the handwheel. There is a groove in the plunger, that if the spring falls into, it won't work, so maybe a cir-clip is required?...

I wish my shuttle had a greyhound on it.

well, I'll keep that in mind. I did figure out the handwheel issue. There is a pin broken off flush that is supposed to hold that knob out. Redrilling will be awkward.