Disco td5 air in fuel system

I need help!
There is air getting in to the fuel system some how. Have tried a new pump (ouch) still the same tried a fresh filter housing and a new air bleed valve and still the same . Hit a wall now cos in my mind if air is getting in diesel should be leaking out when it's under pressure but it's bone dry!
When it's running it's absouloutly fine runs perfect and pulls well!

Does it start OK? Have a search for Injector Seals on here - that's where mine was drawing air from, but it usually makes them hard to start as well...
http://www.landyzone.co.uk/lz/f7/td5-fuel-pump-whinning-bubbling-152661.html
http://www.landyzone.co.uk/lz/f8/air-fuel-system-57012.html

Sorry for taking so long to reply. It is a pig to start. I hate yo say it but I did doubt your advise :doh: sorry. I thought it would be making oil. bUT I was wrong :der: you were bang on the mark. Thank you very much