Hi All,
I think I have cured the leaking decompresser...
First of all I examined the crush washer seating surfaces as Sewerman mentioned in his earlier post and yes they are very ordinary. Mine looks at though the tool used to cut the seats was either blunt or clogged with swarf. To repair this properly the head needs to be removed and the seats re-cut.
Now for the cure... I reassembled the decompresser less the cable and FITTED NEW CRUSH WASHERS OVER THE USED ONES, TWO BIG AND TWO SMALL. I installed it into the head tightening it firmly. I then started the engine and sure enough "Pht Pht Pht" it was still leaking. I then rotated the valve, nothing, I then tightened the decompresser, leak stopped, tightened a little more leak started again, DAMN!! backed it off still leaking, tightened a little more leak stopped. Time to leave sleeping dogs lie...
All I can do now is monitor the situation and see if the leak redevelops finger crossed it won't.
Roger