I assembled 11 more couplers. All worked fine. I had what I consider are a couple of assembly insights, and did things a little differently.
I decided to disassemble ole number 1 myself 'cause now I'm a x-pert!
I did notice that #1 had a wee bit of vertical play on the knuckle. Not much, maybe a couple of thou. But noticeably more than all the others.
When I opened 'er up, I found a wee bit of flash at the edge of the lower "ball catching" hole. Whether that was the problem or not, the flash had to go. So it went. That particular flash cleaning is, by the way, a part of my new assembly method; as there was flash in that location on some of the other couplers.
I reassembled the coupler and the primary problem was gone. So was the vertical play. The knuckle now closes when it's s'posed to.
It was still a little funny, though, in that the knuckle now wasn't enthusiastic for opening. Using a magnet, it would work. But the upside down trick didn't. I put a little graphite inside. Wiggled things around. Removed most of the graphite. Coupler's now happy.
So it looks like Frank won't be getting my coupler to examine. But he WILL be getting an order in awhile.