I tried dismantling the STX "Rapidfire' shifters from my 94 Trek with no success. There are a lot of soft plastic bits in the ratcheding mechanism that just wear out and can't be reached. I bought a pair of slightly older Deore LX thumbshifters from craigslist and they're nowhere near as complex and look even more retro. Plus they can switch from index to friction like the bar end shifters on my normal bike.