I had a look at these fancy papers you are using Gordon & can see why you wouldn't want to be wasting any

Also it came up with this The Roger Maile Colour Calibration CD - The DPA Print Tuner (MAC & PC Compatible) at £13.50
http://www.on-linepaper.co.uk/acatal...NE_Papers.html
which sounds as if it might be the sort of thing that could help
tho if the performance is erratic, maybe you are right and you are pushing the machine too hard for its age