D2 TD5 starting problems

I have the problem that many have tackled on this forum - difficulty to start after a few hours of non use.
originally thought it was the fuel pump as it made a whining sound once the turned on, changed that but same problem, changed the fuel filter and finally the air bleed valve on the filter housing, still no different.
The fuel pipe non return valve was my next option but on removing the connecter from the filter housing there does not seem to be one on this vehicle ( 2002 model ). there is no rise in the engine oil level and the fuel regulator was changed 6 months ago due to leaking. any further ideas ?

Injector seals and o rings need replacing.
Mine had the same symptoms a few months ago. Noisy fuel pump, not wanting to start after being idle for a few hours. Changed air bleed valve, no change.
Symptoms came on over a few days.
Replaced with genuine lr parts. Took a couple of hours to do and perfect since.

Many thanks I will most likely have to do that next but one question was that if the seals or o rings had gone would I not be getting a rise in the oil level ?