Is this the KINGPIN you're talking about or the bottom, outer HINGEPIN? If it's the bottom outer hingepin, ditch the stock threaded ones and get the stainless hingepin kit from tamiya. It uses a setscrew to hold it in place rather than the small threaded part on the pin. I replaced mine in my EVO IV and totally eliminated the problem. Just make sure you grind a small flat spot onto the pin with a dremel so the setscrew has a larger surface area to grab onto.