Ideally, the rebound spring should be unloaded at rest, the top just kissing the axle. So the spring is 5 mm too short, but I am not sure this really matters. However, it should of course be symmetrical, that is the spring on the other side should be the same. One test is to try to twist the spring with your hand. If you cannot do this, the spring is compressed and thus asymmetrical. If you can twist it easily, it is unloaded and the difference might be within the limits of the acceptable. As it is under guarantee, I would have taken it to the dealer for a checkup.
I do not think this is the reason for your wheel wobble. It might be "St. Malvern's dance", a movement inherent of the wheel /suspension geometry of a Mog. They all do that, Sir... At least many, incuding mine. Got better after I balanced the wheels and lubricated the damper blades (which newer cars do not have). So now I can easily live with it, but am planning to install a steering damper.
