Swinging arm

i have been having this problem for quite sometime, but now its have become a bit annoying. when ever i run over potholes, the steering will turn (either left or right). this has never happen to my other car.

now i having problem the steering keep pulling to left side. have been to many workshop, the last one they adjust it to positive chamber. it cure a little, but once a while it will still turn to left ( i am taking on stright road). i am afraid it might cause my tyre to wear very fast.

i just change my absorber (all four). thought it might have cured it. but it did not..

i am now suspicious that the swinging arm bushing might have soft and the one giving the problem.

is there anyway i just replace the bushing alone withour replacing the whole arm? to test it. it going to cost me a bomb if i going to change it base on my guessing only.

is there a way to just replace it and with what type of bushing.

thanks