Er, STI, not SIS. Showing my age… It’s an Ultegra 9-speed something-or-other. It finds its clicks. It just doesn’t pull the cable.
Once I pulled it off the bike, I can see that it’s clearly broken inside. It looks like there’s a little plastic receptacle for the barrel on the end of the cable, and that receptacle has torn and the barrel has pulled through it. I can’t push it back out, if I wanted to replace the cable. It’s close to ten years old, low miles. Really annoying that some little plastic piece has failed and will cost hundreds of bucks to replace. This is what makes retro-grouches.
Sram sounds like a good alternative, if it’s compatible (pulls the same amount of cable) with Shimano. I kind of like the flight deck feature. I wouldn’t care on a single, but on the tandem it is hard to tell what gear you’re in. Seriously considering bar-cons – do they route the cables under the bar tape?