axsatr,

Your vibration @ 100km/h is caused by a missing drive shaft damper, which was not installed in certain units of the first batch 2007, non-iafm model. This is caused by different suppliers for the drive shafts; some had the damper installed and some not. You can find very good posts in motortrader forum, search for "persona drive shaft damper". This problem has been solved in later batches afaik. The symptom is pronounced pedal foot vibration at 100km/h only; more than or less than the speed you don't get the vibration.

I see the car is getting old; it's a good car while it's new but after you have done some mileage on it you can see how badly it's made. Changed mine - you should cut your loss while still can.