First check that the caliper is tightened properly to the frame. If this is not part of the problem then your caliper return spring may have developed an offbalance weakness. You may need to replace the spring or you may be able to bend the weak side a bit to bring the caliper back in balance.

Here is a link to replacement springs I found conducting a quick search.

http://www.ebay.com/itm/Campagnolo-G...ht_3998wt_1045

-j