I fixed mine by removing the diaphragm from the stabiliser valve, drying & cleaning with methylated spirits and a liberal use, both sides, of super glue including letting the glue run in a around the annual ring.
Forgot to say the basic problem was a couple of splits in the rubber diaphragm. If glueing didn't work (it did in my case) would have made a simple replacement diaphragm from sheet of suitable gauge rubber.
David Clay, September 2011