53 Willys,
As far as the Esky servo goes, open up the case top and you will see the tiny metal gear from the motor spinning without engaging the adjacent
nylon gear. Just use needle nose pliers to gently pull the small metal gear up far enough to engage the nylon gear. Voila! Problem solved. No more humming. I've done this a couple of times and flown the heli with success, but I guess you never know when the gears will disengage again. I think it will take a crash to cause the problem though.