When down-shifting my rear derailleur (Campagnolo 10spd) is skipping multiple gears. The problem feels like it is in the shifter as it just "lets go" when I press it. I'm told it could be the G spring. Is it something in the derailleur or the shifter? If its the shifter is replacing the G spring an easy task (doesn't look like it is in the exploded diagram!).
The correct answer to your query depends on the model and age of the system.

If it's an older system from the Record or Chorus ranges, when they were still 10s (pre 2009), then yes, the G-springs are a possibility.

If it's from pre 2007 and is from the lower Campagnolo ranges (Xenon, Mirage, Veloce or Centaur) then it could possibly be a G-spring issue - all of these ranges pre 2007 used a lever mechanism basically the same internally as a Record or Chorus 10s lever - Xenon moved away from that mechanism in 2004/5, Mirage etc in 2007 to a system called Escape.

The G-Spings (AKA the P springs - it depends what letter you think they resemble) are two springs which engage a ratchet. The ratchet is what sets the index interval and if one or both springs fail, or if the mount ring that holds them in place fails, you can get the problem that you describe although normally in these types of lever, if tou have a system that "falls through" all of the gears, the shift in the other direction won't "hold" a gear reliably either.

Levers of this type can be repaired as others have noted. If you don't want to tackle it yourself, we offer the service here at Velotech Cycling Ltd - please drop me an email at the address below, for more info.

Post 2007 and Pre 2009 Xenon through to Centaur all used "Escape". These levers have no G springs, but an escapement mechanism. If that is proving troublesome in the way you describe, the only relaible &amp; long term fix is a complete lever body, Campagnolo part number EC-VL100.

Veloce and Centuar 2009 - 2011 used an UltraShift mechanism. These are serviceable but this kind of issue is very rare - I'd suggest a call in to a Campagnolo Pro-Shop (see the Campagnolo website for a listing) or drop us an email at Velotech - we are the main UK Service Centre - email us at velotechcycling"at"aim"dot"com.

Veloce and Centaur 2012-present - again, a system that works basically like Escape, called PowerShift - the only relaible fix is a new lever body complete, part number EC-CE300.