I don't own the Playseat WRC, but just looking at the picture of it, it seems to be bad by design. You have a plastic mounting base, slid through a thin rounded rectangle tube. Now the tube has its thin side facing vertical, and its thick side facing horizontal. It will be strong for up and down movements (more material = stronger), but it will torque easily from side to side movements (less material = weaker). To put it into better perspective, let say you have a 2x4 wood beam bridged between two bricks. It flexes a lot more when you walk on it with the 4in side (thicker side) is facing up, but not so much when the 2in side (thiner side) is facing up. That is the problem with that seat.
It looks like they upped their design abit though since then, look at the ISR review of the Nascar edition, still wobble though, but probably don't notice whilst driving unlike the WRC.
