I just got back from my small local bike shop. The mechanic said the the right shifter on my old Lemond Zurich needed replaced. I was baffled because I’ve owned the bike for 10 years and have only put about 100 miles on it. Though I purchased it used, the previous owner looked like he kept good care of it.
When I got home I checked on ebay and found somebody asking $200 (!) for a pair that are scratched and worn. I did a little more searching and came across this page on the old Sheldon Brown site of mentioning a guy (Jim McVey) who rebuilds them:
Jim has a Facebook group page too. I’m sent Jim an email and I thing I am going to give his service a try. He says that in most cases the lubricant has dried out in the shifters and usually no parts need replaced.
Getting the shifters rebuilt seems to make the most sense to me ($60 for left and right shifters) but I’m curious what you all think.
The grease in Shimano shifters can get stiff/thick with age, and prevent the pawls from engaging the teeth, thus making the shifter not work one way, but it will shift the other.
A big blast of something like White Lightning Clean Streak, followed by a blast from an air compressor, followed with some heavy spray lube usually fixes this problem. It is best to pause between those steps to allow the cleaner to soften the grease, the air to help evaporate the cleaner, and the new lube to penetrate and set up.
Call Frank at Squirrel Hill BikeTek. I has the same problem and he told me the cable frayed end falls in there and jams. He wanted to fix mine but I ended up replacing w//ShimErgo.
Edit: but wait before you do anything contact Shimano. There is definitely a design issue there. Who knows, even out of warranty they may help you.