Dyson DC01 without suction?

I have a Dyson DC01 Absolute which makes all the right noises but is short of suction, both through the wand and the main cleaner. I have replaced filters and read previous posts re blockages. I have had the thing apart and checked all the airways for blockages. I have replaced the drivebelt. But it still won't work. Do I put this down to old age (the Dyson) or is there a trick I've missed?