Y61 fuel bleed issue

Hi all, have a 00 GU ZD3.0 (old skool) which has recently had an engine rebuild where it was out of action for a little over a month, since getting it back when I park it on a hill with front higher then the rear the fuel drains back into the tank behind the fuel filter. When I go to start it it runs until the head of fuel between filter & pump/injectors is exhausted and then I need to prime it again before it will run.

Only happens when parked nose high on a slope about (30 degrees I would guess).

Mechanic has checked all clamps and replaced any old ones with new ss worm clamps there are no visible fuel leaks, filter is tight and water sensor block is tight with new seal.

Does not do it when parked on the flat or nose down even when left for a few days.

Any suggestions would be appreciated, mechanic is getting a replacement primer assy in case that is the issue.