Tail servo
 

I am new to the hobby and recently purchase a used trex 450 pro,the seller said it was all fine and flown prior to posting,when I checked the heli I noticed the tail servo binding at full rudder left,I tried turning down the end point to stop the travel,but the servo then became extremely slow to move,is this normal,though I suspect not,or have I done something wrong..I am extremely new to the hobby ad am having problems understanding so much information about so many topics ,and sometimes conflicting advice on internet searches..can anyone please advise.