My series three started knocking violently out of the blue taking off at a light, I can get it going if I let the clutch out very gently, any amount of welly and there's a violent knocking sound. I thought it might be the gearbox until I noticed the ball joint where the rear suspension top link joins the diff has lost its **** (see attached). Would this cause such a problem or does the gear box have to go as well? Also, is there a kit I can get to sort out the ball joint?