Campagnolo Ergopower Chorus 9 inaccurate shifting My Chorus 9 Speed Ergo-power (~2005) got inaccurate during shifting. The local bike repairman couldn't get the dérailleur to shift properly.

Sometimes the chain don't jump down or up after shifting. Some gears are skipped and the pressure points got weak. 

What parts do I need to replace? Is it maybe a better idea to replace the whole Shifters with a available new 9 Speed Ergopower like the Xenon?
The Ergopower shifters have a part called G spring that eventually wears out. The symptoms are inaccurate shifting and less sharp clicks, just as you are experiencing. The part is still available, not expensive and relatively easy to change.

I would not replace the shifters with Xenon, as it is generally much lower quality and doesn't allow downshifting multiple cogs at a time like other 2000s Ergopowers.