This is a question for the experienced Campagnolo users out there. Sorry for the long post, but I wanted to describe the situation accurately.

I've got a second hand 10 speed 2008 Campagnolo Record group that I'm using on a Colnago Master build. I don't know of the prior history of the group set, but judging from the worn rubber hoods it has been used for quite some miles. I'm having a problem with the rear derailleur shifting performance, and I'm suspecting that the shifter is simply a bit worn and needs a rebuild or a body replacement. Problem is that this is the first Record 10 speed I have ever used, so I don't know how a new one should behave, maybe it's worn, or maybe it should behave the way it does. I have a brand new 11 speed Chorus group though on another bike, which I can compare to.

While a relatively new home mechanic I'm quite confident when it comes to rear derailleur installation and tuning, which I've done successfully on a number of bikes and varying brands. I've done the hanger alignment (using Park Tool's alignment tool), shift cables are new etc, so all the standard problems are supposed to be out of the way. I have double-checked that I've installed the cassette spacers in correct order.

Despite this I now have a problem I've never had before with a derailleur: when I find the best cable tension for indexing the derailleur has a tendency to move too far between cogs -- in both directions. I can shift through the whole cassette in both directions without mis-shifts if I'm really careful when operating the shifter and stop the hand action as soon as I feel a click (which is much softer and less distinct than in my new 11 speed Chorus by the way). But still, when I shift from the largest cog to the smallest, about half-way through the derailleur has went a bit to far and start rubbing on the next smaller cog. The same counts for the opposite direction, shifting from smaller to larger cogs the chain starts to rub on the next larger cog. It's like the shifter would be indexed for 9.8 cogs rather than 10. What I think is happening is that the derailleur moves a bit extra distance after the click due to that my hand doesn't stop the pushing action *exactly* at the click.

I have noticed that I can with the thumb button and the lever release/pull cable and move the derailleur quite a bit without causing the shifter to click (say 2-3 mm sideways). I use that to manually trim the derailleur when I hear rubbing, so the shifting is certainly usable, but I suspect that this is not how it's supposed to be. I'm guessing there should be some springload or something to make it return to its neutral indexed position, but I'm not experienced enough to know. My 11 speed Chorus have louder and more distinct clicks, and doesn't have much if any manual movement between the clicks.

So my question is, is this a symptom of a worn shifter, or something else? If worn, what parts need replacing? I know it's quite tricky to rebuild (I've seen the videos, it would be an interesting challenge), but if I need to replace sort of everything I could just get a new EC-RE200 replacement body which is not too costly. The most frustrating part is not knowing the cause of the problem, or even if it should be considered a problem with this groupset.