GGH20 rear suspension question. Torsion beam problem, or something else?

I recently bought a GGH20. It came to me lowered, on coilovers, and the ride was way too stiff for my liking, as well as the front airdam touching down regularly and making a hideous scraping noise.

I raised the coilovers to full height, which was a massive improvement, presumably because it allowed the dampers to use their full stroke without hitting the bump stops. However I then noticed that the gap at the nearside rear wheelarch was less than that at the offside rear. The spring on the low side was not broken, so I assumed that it was simply weak, so I took the plunge and bought a whole set of new, standard suspension. 

Annoyingly though, after fitting the stock springs and dampers, the difference in the wheelarch gaps at the rear remained as it was. So it just goes to show one should never assume! 

Could it be a problem with the torsion bar? I'm aware that some torsion bars are adjustable for ride height on either side. Is the Alphard's? I know nothing at all about torsion bar suspension, so I'd appreciate any feedback. Could it be a failed bearing or bush? There's nothing in the way of unusual noise or sensation from the suspension.