In case you're still interested... Canon serviced it and said that they "Readjust exposure and shutter speed to standard. Clean sensor". Sent it back. It appeared fine taking an indoor shot at high ISO so I was delighted. Next morning took and outside shot. Also OK. Took another - not great and in AV mode it had selected the SAME speed despite a significantly darker scene. So I played around and it looks like the meter is selecting an appropriate exposure at the FIRST shot and then just not seeing any change in light as I move from indoors to out, or vice versa. In other words they have done nothing and clearly not tested what they thought they had done. It's all packed up ready to go in the post back to them on Monday - ho hum what a painful saga this is turning out to be. Wish I could find somewhere selling unused old stock of the Mark 1.