Well, for £17.50 you can get a valve block rebuild kit here:
Range Rover P38 EAS VALVE BLOCK Diaphragm Repair on eBay, also, Range Rover, Car Parts, Cars, Parts Vehicles (end time 29-Nov-08 07:57:55 GMT)
and for another £93 you can get a compressor rebuild kit here:
Range Rover P38...