I might be wrong, but I think "6400" group is Ultegra 8spd '91 - '96

If that's what you have, and you can get the "sticking" one working okay with the "solvent followed by lubricant" trick, then I believe they'll probably hold up and serve well for many years. No need to replace the, not unless you've got money to burn or just luck up on a fantastic deal on some newer ones.

It's been about a year and half since the last time I had to douse mine with lubricant. Here's a pic of mine, taken after riding in the pouring rain up to the top of Mt. Mitchell. They work just like "buddah".





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