Bicycle Mechanics - How to take apart Shimano indexing bar end shifters?

I have a pair of 8-speed indexed shifters, well-used. I moved the selector to friction mode, and it felt like something snapped inside, and now the selector moves freely with very little resistance, and it moves all the way around.

This means that the shifters are stuck in friction.

I took them off the mounts, and it looks like the parts are press-fit into the lever or something like that. I can't figure out how to get them apart.

Obviously the selector was moving something inside of the shifters, if I can find that thing and move it back into place, I should be able to get indexing back.

Does anyone know how to get at the mechanism inside?

Actually, it seems that I figured it out.

In order to get the guts out of the shifter, I had to break off the black plastic cover. After that, everything is threaded on and it is pretty obvious what is going on. I now have indexing back.

It turned out that the little selector (the one you use to go from friction to indexing mode) had stripped and was no longer moving anything, which is why it was spinning freely. Once the unit was opened, I saw that it was moving a nut which tightened the indexing stops against the springs. I was able to turn it with needlenose pliers, and now it works just fine.

You shouldn't have had to break off any cover. Shimano's web site has schematics which show how to assemble/disassemble the units.