I had a fellow contact me after his LBS told him that there were no parts to fix his 1990s Trek 520 3x7 skipping without building a new rear wheel and going to indexed bar ends. This after they replaced the chain and he experienced pronounced skip.

I test rode it and it was cassette skipping, initially.

You guessed it...Uniglide. I told him that we could replace the freehub body and the cassette with modern 7-speed stuff, and it would stop rear skip, but might not on the largest two chainrings which had a lot of miles on them. But the parts were only $50 for the rear, so we went for it. Shifts nicely, however the skip is now on the chainrings, but under heavier torque.

I have replacement chainrings (half step, as he prefers it) on order. And the lessons are the same. High miles on drivetrain with no replacements = chain wear. High miles on worn chain = cog and chainring wear, too.

The good news is that he'll have the bike back to original spec for significantly less than the LBS quoted for a 9-speed change over. PG