after putting together a couple of these alz380's, one converted to 420 now with every upgrade possible, I had a hard time getting the tail pitch control krank arm to ride freely without loosening the main fastening bolt to unsafe levels. Not one to be deterred from modifying things to make them better I did two modifications in order to free up the control arm so it would not bind and be hard to move back and forth, when the bolt was tightened to proper tightness (wrist tight as most builders will do).
Step one was to chamfer the pitch links on the side where the screw head is. The screw head will mash the brass inner sleeve ever so slightly as it is being tightened flaring it and cause binding in the link's hole. Did this on my align 450 some years ago and figured that was the only one with the problem.
Two; take one of those washers from the kit that is about 2.5x4x.1mm and put it inside the bearing housing of the pitch control crank where you will see a brass spacer. To remove one bearing I put the crank arm in a freezer for ten minutes an popped a bearing out while it was cold. Put it all back together with the extra washer inside along with the sleeve and check after you give a good firm twist of the hex tool. Test it without the arm on the slider at first.
I wondered why guys have tail wag often on the d380's and it's likely because of binding from the two parts mentioned. If it isn't as free to move as a well oiled wheel it's going to be a problem and possibly burn out a servo prematurely.
I don't know if g380/420's have this problem but in case you own one and run into tail wag/binding you should examine the same parts as probable cause.