Top tubes on Italian bikes got shorter over the years, part of that reason was the research done by C.O.N.I. for the Italian Cycling squads and that research made available to the Italian frame builders.
Take the existing Campagnolo head set out of its bag and inspect the parts, Best suspect is the lower race and cup, if you see any dents in the bearing track then that is your answer. Time for a new headset. (some mechanics know how to extend the life of these but if you do not have the tools at hand to assemble it and take it apart numerous times, sell it on ebay and show the good and the bad, usually some parts are still useful and have value)
Use those proceeds to buy the headset presented by gomango. Locate a shop that understands vintage bikes and has the tools, preferably a Campagnolo tool chest.
Then Sprint into Spring.