It could be, but there's something you might want to try before looking into a new one.
Take out your tail blade shaft and bearings. Lube the bearings with something like One Lube (slick 50 product) by squirting some on your finger and thumb and rubbing it into the bearings. Then put the bearings back in a re-seat them. Check the shaft for rough spots and smooth them out with fine sandpaper (600 grit should work). In fact, it won't hurt to lightly sand the shaft anyway. The lube the shaft the same way you did the bearings and when you insert it back into the bearing, make sure it spins freely. Any binding, no matter how small, will cause problems with these tiny tail motors. After you put the gear and rotor back on, you might want to dry the end of the shaft before putting the tubing back on.
I know these are designed so that the shaft fits tight in the bearings and the bearings spin, but the fact is that the tail assembly isn't precision and the bearings don't always align properly when they are seated in it. It's OK to have the shaft spin independent of the bearings and the bearings spin also. It hardly ever will, but if it's allowed to, the tail blade will spin more freely all the time. It helps with alignment.