RE: Lazy erratic servo action.
Well, they are laying on their sides, so all the electrons leak out of the potentiometers and puddle up against the inside wall of the servo case! You're probably lucky they didn't just short themselves out right to the circuit board, the instant you plugged them in! Sounds ridiculous, doesn't it? Well it is.
Maybe you should check the connections at the receiver, to see if there is some reason they are coming loose or getting contaminated during storage. Is there some rust / mildew / corrosion in there that gets a chance to "grow" during the period of storage? Something like "black wire disease", where the wires of the negative lead of the servo plug become tarnished?