I have a stock '76 Precision Bass, maple neck. The neck is bowed very slightly. I can tighten the truss rod and get it exactly how I want it, plays very nice. However, over the course of 3-4 weeks it will eventually return back to where it was before the adjustment, slightly bowed. I can make the adjustment again, but it will become bowed again in a few weeks. I have repeated this procedure probably 5-6 times in the 10 years I've owned this bass. I am concerned that the repeated tightening of the truss rod will eventually max out or strip the threads. Why does it keep becoming bowed? Is it possible that the nut is slipping or partially stripped? Any suggestions?