i am in the middle of sorting a similar problem out myself i have replaced the rear half of the 2 piece tailshaft but have not balanced it yet with the front half, so im not 100% sure if this is the problem or not. but i am in the process of replacing all suspesion components including steering rack mount, radius bushes, front and rear camber adjustables.... then full wheel alignment, im going to see if this has any affect on the cars driving, if not im going to start with the tailshaft balance then maybe a steering rack overhaul if they think its needed. suck but there is nothing i can do about it but try to eliminate the sources 1 by 1.
imchecking all the little thing slike tyres aswell on the way but going to wait till after wednesday to see when it all gets done.