Hi Fellow X5ers!

Ok my issue is this....

Started a few months ago now but my x5 3.0d e53 (2002) really hates to start from cold! takes roughly 3 turns of the key cranking for long periods of time each time.

Took to the garage and had full set of glow plugs replaced
= No difference!

Replaced the 5yr old battery with brand new premium batt
= Cranks faster but still no difference!

Took to garage for diagnostic and comes up with "low rail pressure on crank" garage replaced Diesel pump and fuel filters
= No difference!

Took to garage again still showing "low rail pressure on crank"!

Personally from googling around im thinking it could be a sticky injector?
Any ideas guys? Any help much appreciated....