The mileage is 150,000km. No service history. So Rocco was right: the shimmy comes around 80km/hr but it becomes much more pronounced at 120km/hr and up. I am not sure what's causing this. Any ideas? Anyway, I am taking the car to RMP Motors again when I have time.
There is also shake in the steering wheel when braking at high speed. This is more than likely is caused by worn out thrust arms.