An ongoing problem I've had is that my derailleur sits pulling to the right...when aligning it manually all is OK...I've set the high and low screws and have no effect on this nor does the third screw ( spring? screw). All the other bikes in my building's rack have nice straight sitting derailleurs and don't seem like they want to jump of the cogs as mine do. I've enclosed both high and lows gears with the chain sitting on the largest chain stay. Is there an adjustment I'm missing.?