Don't know if this helps.
I sometimes had a vibration problem with my V6 mondeo but only at a certain speed (+/- 5 mph).
When going faster or slower there was no problem.
This was simply down to tyre pressure difference in the 2 front tyres (even 1psi difference could do it).
All my mondeo alloy wheels are bad for holding tyre pressure, I've tried new valves, reseal tyres etc, but it didn't work.
I now keep checking the tyre pressures weekly - no more vibration problem.
Tom, November 2008