I have encountered this twice this year now and both on the right shifter, so on the rear cassette shifting. Firstly on my 6700s and seeing as I had used them for 2 years I decided to get some 6800s. Now I should say both sets I had were second hand off ebay so had seen use before I had them. The problems are similar with both, the shifters can still shift a little, 5 or 6 shifts but then no more. Currently on my 6800 I can shift 5 times down and then I can no longer hear the clicks, the levers just move without engaging any more cable. I have tried the first step quick fix of spraying it with GT85 and then using an air duster to get rid of the excess lubricant fluids. This has not helped. I'm 95% sure something has worn in the shifter but just before I get another new set of shifters just wanted to ask if anyone has revived their shifters from a similar predicament?