2457XT

I'm pretty sure they are independent of one another - as the cannisters that sit on the rear strut legs are a purely pneumatic system and don't adjust the rear ride height until a few miles of driving with a load in the rear - no fancy electronics at work at that end. Whereas the motors on the headlights adjust the beam pretty much instantly as soon as the lights/ignition come on.

It does seem weird to have both systems in place It concerned me as I am considering replacing the stock SLS rears with Pedders units and I was worried about the MOT aspect as you said. I got my son to jump around in the back of the car while the lights were on and you can hear the motor whirring in the headlight units to adjust the beam height - so all should be good to loose the SLS struts and stay legal. :)

The HID light units fitted to the SG models are self-levelling themselves, so losing the self-levelling rear struts is not an issue.

A few of the guys on the forester.org forum have gone the Pedders route and they seem pleased with the results. I need to replace the struts/springs on my own vehicle in the near future and I am intending to use the Pedders lowered package too.