What grade of oil are you using in the car? The older the car the thicker the oil needed (because all the clearances increase and this also increases the bye products of combustion leaking into the oil system and contaminating it) and gradually we find semi synthetics or even fully mineral oil can be better as the engines age (not seeking a debate on this - just stating what we have discovered over the years - different opinions help yourself).
Also if a dual port waste gate or a waste gate bye pass/bleed valve has been fitted or it has been chipped (basically anything that increases boost pressure) then more pressure will pass the pistons and increase the amount of oil mist that the breather system has to deal with, inevitably burning a little more than it should standard.
1000 miles/litre is not excessive for this age and mileage friven resonably quickly.
Hartech comment above
I will check the airbox and oil grade tomorrow, I do have a DPW but only run it at 0.8 bar
I have been driving it fairly hard down to portsmouth and back .......on the back roads
