well we finally broke down jonnys block at the weekend.
we found that the offending item was the front plate water seal, a small deformation of the wall to the water ways.
we also found that the rotor housing has some very deep scoring in it??? ive inspected the seals and there doesnt seen to be any bits missing, so im guessing that there must have been some crap in there??
anyhow just got to clean and inspect the parts and see what needs replacing.
will keep you posted on progress.
N