Bad repeated lurching motion when accelerating

[Horrgakx]

Hi - for a couple of months my A8L W12 has had quite a bad repeating lurching motion when setting off from standstill and there is a grating noise when going over speed bumps. The garage diagnosed worn suspension bushes (they call them "Front Arms" on the invoice) which were replaced in January. But it still happened.
So they diagnosed further that the "Bottom front arms" needed replacement so they were replaced today. I picked the car up and guess what, still exactly the same.
So I've spent £1,600 so far on suspension components and it's no better. Worse, I'm looking at 3 weeks to get it back in.

Is there anything else I need to get them to look at? Without part numbers I don't know exactly what they've changed. I will email them now and ask if they can tell me.

Thanks.