Can anyone help with an issue I have with a non return valve on a 1983 SWB Series 3 2.25 diesel... The valve sites under the intake manifold and a pipe then runs from here across to the brake servo....and currently it's not doing what it should ,.. I'm convinced it's broken, but cannot get the part anywhere in the country as it keeps coming up as obsolete. (part no. C37474 just to bore you to tears...) Can anyone help or enlighten me as to what it does/is or does anyone have one?????