Had a brief drive of another 500 (2012 twin air) the road was a bit uneaven and noted a definite clunk from the rear, couldnt replicate by bouncing the car but sounded like a bush issue, lo and behold the last mot had advisory for rear, top bushes. What sort or cost is involved in replacing these, and it it work looking at polybushes? (I have a subaru currently on which bushes are considered disposeable)