My tri bike is set up with Campy record 10sp bar end shifters. While riding this past weekend the right shifter (controls the rear derailleur) will no longer maintain the tension on the rear derailleur cable. I can no longer shift up to a larger cog on the rear cassette unless I physically hold the shifter in place. I unfortunently have a race this coming Sunday and I need to get it fixed ASAP. I'm pretty sure the issue is with the shifter itself. Is this something I can tear down and fix? Do I need to purchase a new shifter? Can you even buy a single shifter or would I need to get the set? Any suggestions? Thanks!!