Tracking issues and worn suspension springs

[gazza1286]

Hi
I recently had a 4-wheel alignment but my Roadster continues to have tracking issues. Letting go of the steering wheel on most roads, regardless of the camber, causes it to rotate to the left by around '2-3 minutes' with the inevitable drift towards the kerb. I've swapped the front wheels around but it's still the same. Both tyres have plenty of tread (Nantang - no blemishes). I'm therefore confident that the tracking isn't due to the tyres.

I know that the front springs were highlighted as an advisory on the last mot from June before I bought the car (rust on both) so I thought I'd investigate further.

I've measured the distance from the centre of the wheel to the peak of the wheel arch all round. The rear two are identical. For the front I've found that the offside (right) is sitting around 1cm lower than the left. Measuring from the ground to the sill at the jacking point confirms this discrepancy.

So I appear to have worn front springs. Looking at them, the gauge of metal on the coils is much thinner than on most others I've seen. Is this a common problem?
If the offside appears to be sagging more why would this cause a drift to the left?
I will be replacing them - can anyone recommend a particular brand (standard height). Are there any other measurements I should check?