I have purchased thru Prevost as well as Kaman Industrial technologies/I don't think one can buy less then the entire valve thru prevost?/kaman has the spool assy. with orings for less then 15.00 dollars/ the last valve I bought from prevost was 160.00 dollars/the spool valve replaced on my H45 #1855 fixed the leak and was # nrg 54237 nitrile spool assy k71/I compared it with the spool valve that I took out and it was identical/I tried to buy just the o rings but they would have had to try and match them up,as they could not cross reference them/joe