
You can guess those balls are meant to be part of a race - explains the noise !!!
By good fortune, and the fact I hate to throw anything away, I had a pump from a 2003 Range Rover L322 TD6 in the shed with worn piston seal but a good motor and crank. The Dryer part, black part pictured below below, was different to mine with different air fittings but the motor part was identical so I simply swapped my dryer / cylinder assembly over to the new motor.

New piston seal fitted from http://www.ebay.co.uk/itm/151019274218? ... 1439.l2649 for £35 a quick re-assembly and she is back riding high. Took about 30 seconds to lift the old girl back to ride hight after being down on the bump stops.
This is the old seal removed from piston..

And the piston with old seal fitted.

If your motor is ok then fitting a new seal is only a 5 minute job when you have the pump in your hands- mine was made easier by the fact it is relocated to the rear right cubby due to the LPG conversion.
So bottom line is if you are getting the "AIR SUSP" fault coupled with the pump running excessivly and you have no obvious leaks then a seal is worth looking at.