My family and any college friends who are reading me remember the time when I was up to owning three bicycles - my Dad's resurrected Sport-touring bike from the early '80's, a mountain bike, and my LeMond. I did almost all of my own maintenance and repair, and between the overhaul I gave the old Trek and the beatings and upgrades I gave my mountainbike, that came to a lot of maintenance and repair.
I brought the LeMond with me when I came up to Albany for this show. I was riding it to commute some, and started having trouble shifting. So I looked over the drivetrain and it was filthy. Really filthy. Filthtastic, even. So I bought some tupperware and a can of degreaser, unmounted the chain and soaked it for a couple days, cleaned the drivetrain components, remounted the chain, lubricated everything, and gave everything a tune. Then I went riding, and all seemed good. Until the drivetrain started skipping. Stopped, looked things over, couldn't find a problem. Rode some more, and fell. I was popping out of the saddle to accelerate and I broke the chain. Dammit.
Anyway, I remounted it and then went to the local bike shop because the link was a little stiff where I reconnected it. They couldn't find a problem, even after cleaning everything even more, but they didn't charge me.
So I went riding again a couple days later. The chain starts skipping again. Still can't find the problem. Chain broke again. I remounted it again and went home (shop was closed.) Since then, I've re-found where I reconnected the chain so I can find it again at the shop when I get it fixed. But I thought that this was probably too much of a pain in the ass for such a common procedure, so I did some research.
It turns out that when you separate a Shimano narrow or super-narrow chain, the pin that holds the links together is destroyed. It's destroyed in a way that can't be detected without a really high level of magnification, but if you don't throw it out it will fail sooner or later. This isn't a huge problem because Shimano manufactures special replacement pins, but while I knew about those at one time, I'd forgotten. And I certainly don't carry any right now.
The other problem with reinserting the old pin is that it warps one of the links in the pair it holds together. The special pin comes on the tail end of a guide thingy that (I think) prevents this problem.
Other brands of chain have a breakable link that allows them to be removed and installed without messing around with tools. But apparently that's too simple. So it's time to get some special replacement parts. Yay.