I also have a 12 year old set up from Demco. It has one tang on the tow bar eng that slips into two tangs on the base plate. These tangs have opened up several times and I finally added 1/2 in backer plates on either side to keep the base plate tang from opening up. It looks like the three tang design would prevent that. My conclusion from observing this is any slop in those tangs make the side to side motion worst. Steel in pure tension is very strong its the bending modes that weaken due to the slop in that joint. My only suggestion is to check for worn or egg shaped pins, holes or excessive slop between tangs. What was the tow bar rating and what did your tow car weigh?