The area labeled "vr2" is a micro adjust for steering centering...in AM devices they sometimes needed to set the steering center by using both the board item as well as the TX dial.
If what you say is correct and you've tested for pot function:
1. Set TX "st trim" to 0-center
2. power tx
3. power rx/chassis and with very slight movement try using vr2 dial with a flathead driver and see if you get any response difference.
tagrgetingxmod does have some valid points as well...it seems you have covered both our queries though.
One other option which is a bit left field:
When i used to do 2.4Ghz/asf swaps into AM chassis I would sometimes get the motor leads backwards and i would get a similar "full throttle locked steering". I realize that in your case this was caused by an impact but you might consider swapping the motor leads to see if that does anything.