These type of things are often a puzzle to begin with. Considerable time has to be invested to gain a clear understanding of what is happening. The hope is some of that time can be recouped on the next one. Sometimes it works.

I could easily become an addict and spend all my time testing & measuring. How stuff works has and always will fascinate me. Like many who post here my fascination has become my livelyhood and in turn led to the employment of others and the responsibility that goes with it. Time is the enemy.

The pump was fitted by the tech who did the engine transplant. He was available, I was not. The logic in my desicion was to fit the vehicles original pump that we presume did not have this fault...but maybe it did.