I've had this too, and I run 8 speed Campag on my Denton road bike, and a new cassette and chain together fixed this instantly.
Sticking me neck out here, but if you are using the original Campag 8 speed setup (top left in this link) http://branfordbike.com/articles/casset ... s-pg60.htm
and not the later Exa Drive setup, then in theory you should be able to remove the cassette and reverse the largest 2 cogs so they are 'inside out'. Not the best technical fix I know, and it probably won't do anything for the smoothness of shifting, but if it makes a difference then you are closer to confirming the cause of the problem.
Just a thought...
Thanks for this suggestion - I was getting excited about it for a minute! Sadly, it is an exadrive freehub, with the slightly thinner single spline for correct cog placement - I suspect that this means that they can't simply be spun around.
However, found another Campag wheel with a 9 speed cassette on it lurking in the back of the garage - shall give this a try and swap it over, using the 8 speed spacers from the current set-up which is giving me the jip. The 9 speed cassette looks to be in much better condition.
Rossin Concept MTB 1990 - Full XTR M900
Litespeed Ocoee Titanium MTB 1992 - Grafton / Bullseye / Syncros / XTR
LeMond Z Team Issue SLX 1991 - Full Corsa Record / Sigma
LeMond GAN Team Issue GLX 1993 - Full Dura Ace (7400)