Lexus main dealer quoted over £1600 for this job so I looked around before I let them on it. Then whilst I was having my tracking adjusted (darned potholes) and it was on the ramp the local exhaust centre asked me if I knew I had a leak (it was obvious considering the baubling noise) and did I want them to fix it. I had both sides fixed and they charged £20.00.
It is now quieter than I ever remember it being. :o)