I took the pipes from the filter to the turbo and from the turbo off and they have pools of oil in them. The resonator does too. The breather pipe also had lots of oil in it. I checked the turbo for play and there is none. I'm thinking now that the issue is from the breather system but I can't find much information on this and there doesn't seem to be a ventilation valve. Anyone have any idea why so much oil would be drawn from the breather?

Breather pipes always dump oil into the intake, it's not unusual to pour a cup of oil out of the intercooler on a 10 year old diesel, it's not ideal but it is normal.  You can fit an oil catch tank if you want to stop it, but it doesn't make a noticeable difference to running in my experience.  The intake system should be sealed though, air (and oil) shouldn't be able to leak from it.

Thanks for this, so it's better really to try and fix the leak. The ford dealers quoted me 513 pounds for the doser valve. I'm guessing that they're quoting for the whole cover and that the valve is not available on it own. There are some on eBay so might have to take a.chance on one of them.