Hi Guys, been a long time follower so hoping I can gain some of your wisdom with an unusual issue:

Have a problem with my 10sp Campy chorus shifter, the symptoms are an RD that will sometimes shift perfectly from gear to gear through the entire cluster and sometimes skips too far or not far enough (usually around the middle of the cluster) which makes the chain jump about creating a nasty noise.

The shifter seems to be pulling differing amounts of cable when I click through the gears? Has done it since I bought the shifters 2nd hand and even after overhauling them twice (1st time i didnt tension the coil spring correctly but got it the 2nd time).

When I engage the lever very slowly, the chain sometimes shifts before the 'click' and sometimes after, regardless of the tension on the cable. To test this i've over-tensioned and under-tensioned the cable with the expected results.

While riding its only a very sporadic issue and I overcome it by shifting up two cogs then back down one and it usually settles where I want it but something has to be wrong for it to happen in the first place...

So far I've replaced the RD, Cables, chain, correctly re-positioned the shifters on the handlebars, checked the routing, replaced the cluster, replaced the hanger and had it aligned by the LBS (they have no solutions for the issue...) so I'm wondering if anyone has any other ideas?

My frame is a 2007 Bianchi 928l b4p and all the rest of the groupo is virtually new (New record cranks, RD, chain, campy cables) except the Chorus shifters which have only just been overhauled.