I've seen doing this mentioned a couple of times, and it seems like this is something I need to try. I have 9sp Tiagra levers on my Novara Randonee, and I've been having a hard time getting the rear derailer to drop onto the smallest cog. I pulled, cleaned and reinstalled/readjusted the derailer, same problem. Then, I needed some other work done, so I added it to a list of things I needed done, and had my mechanic adjust it. He reports that just like I said, it's hesitant to drop onto that last cog, even though the limits, tension, and B screw are all set properly.
He said either the derailer or the lever is failing, and since he said that the derailer drops down OK if he operates it by hand, I figure the lever has a little shmutz up in it somewhere.
So, I have to retape these bars anyway, can somebody tell me where to spray into these works (and are there covers to remove?) while I have the tape off, to have a chance at flushing out whatever's causing my problem?