Gary in post 5 brought up something that most folks don't think about. When I was working IMAA shows I saw a lot of mystery crashes that were traced back to Ys and leads being dirty or coroded. Big Giant scale planes don't get flown as often as smaller planes and they just sit in the hanger. Time for a show and they come down, get checked out and flown. Long servo leads don't get pulled or cleaned and you have a mystery crash. If you have leads and Ys it's a good idea to once a year shoot them with electrical terminal cleaner and plug them in and out as Gary mentioned.
In my case I quit using them. Lead cleaning is something no one does. I solder extensions onto my servos and forget them. Ys I haven't used in years. A friend owned a hobby shop and there was a rash of bad Ys being brought back to the shop so we tested a bunch of them, both JR and Futaba. Almost half of the Ys on the wrack were bad. I have never used one sense. We figured they didn't move very much and may have corroded?? You can have a bunch of bad Ys. I have also had a bad switch that caused a servo to go nuts and a bad RX. It can be more then one thing going on.