We have an older Burley Bossa Nova tandem with suntour barcons and the front derailleur no longer holds its position. I tried tightening the screw (with the little flip-out ring) on the right side of the barcon but that did not seem to help. I managed to take it apart enough to remove it from the bar, but have not been able to take it apart any further. Is there any maintenance/cleaning I can do, or parts that need replacement to get it to hold again?