I sold my 2006 Vectra SRi because it was impossible to get rid of the vibration through the steering wheel and the frame so I don't know that I can help, but this gadget was highlighted in an email-shot I just received and I don't know if it would be any good for you or anyone else?

http://www.toolbay.co.uk/Gunson-Tool...ber-Gauge.aspx