Thanks Fitian,
I have sorted the problems (i think). I disassembled and cleaned all parts. Reassembled using oil on the seals, this seemed to make a better seal. vacuum tested the unit and found that all the bolts blocking the other inlet and outlet holes and the bleeder hole on top were all leaking air substantially. Refitted them all with plumbers tape and retested. Vacuum tested ok, no leaks. Fitted to car and bled system through. Started car and drove it. No hiccups or power loss. The old OEM filter must have been pretty blocked (or the OEM housing leaking air as well) because the idle rpm on the car had been dropping off and now is back up to where it should be.

I hope that the CAV filter ass'bly can take some vibration and so forth because I am taking it bush this weekend.

Also dose anyone know how well standard plumbers teflon tape reacts with diesel and biodiesel?

If it fails then it will be back to square one.

Thanks again for everyones help

Sam