My wife's bike has an STX derailleur on gripshift shifters. It actually shifts ok, but there is a metric butt-ton of play in the derailleur pivots. Is there anything that can be done to refresh it, so it stops sloppin' around, or do I just need a new derailleur. We're trying to sell the bike so I don't want to redo her drivetrain, and selling it with the slop has been hard.