I raced a TRF501X for the entire 2007 season. I soon realized that the kit shock shafts were letting the otherwise excellent TRF shocks down so I replaced them with Yokomo shafts. After that, the shocks were brilliant ! I only needed to replace the O-rings once !
For 2008, I got myself a nice new TRF501X WCE with the new Tamiya gold nitraded shafts. During the first race with the WCE, I also noticed the "gold" fading on the shafts. On top of that, I bend a front shockshaft coming down from a large jump !
After that : i dumped the Tamiya shafts and installed the excellent Yokomo shafts again. Never had a problem since.
My advice : Dump the crappy Tamiya shock shafts (steel or nitraded) and put in some Yokomo shockshafts.