You have identified a leak in one of the spill pipes & that is the most likely reason air is getting into the fuel. The fuel transfer pump inside the injector pump is not self priming, so any air lock will stop it pumping, hence the primer pump on the fuel filter.

I would change ALL the spill pipes & if there is still a problem, install some clear tubing between the filter & injection pump looking for air.

Update(although a bit late in updating, lol)

Filter housing head(primer pump) changed.

Rubber hose from filter to FIP(lucas) changed.

Now, starting has a peculiar issue.

1) It starts when it is in zero slope.

2) It keeps spinning without firing when it is parked downslope or upslope. In such conditions, if it is primed 1 or 2 times, engine fires instantly.

Kindly throw in some pointers.

EDIT: i have attended the diesel leak in the 4th injector. Everything is as good as new.

By the way, what is the black valve in the plastic hose that connects the filter outlet to the FIP inlet?

Edited by fordfanindia on 08/08/2013 at 05:05

It seems to need a more viscous fuel supply, this happens on Hdi engines when the HP diesel pump is worn, it could be wear in the injection pump but the old ones don't usually suffer from that problem - except some BMW pumps.