Thanks for replying, I have ordered a new unit and the O-rings, also one of the two main fuel lines has a small filter in a brass connector of which one side screws directly into the metering head.
This was full of rubbish to the extent that I cound'nt blow through it. Have cleaned it with carb cleaner. Not sure if it is the inlet or return.
Also ordered new O-ring for below metering head as this was perished.