Aye it looks easy enough to replace that part - odd, though, is that the hose going into the inlet manifold was covered in black oil on the underside after a run.. not quite sure where it's coming from, unless that hose just isn't sealing properly on the inlet manifold.
Would you completely fill the fuel filter with forte, or mix forte & diesel? I have a fuel filter waiting to go on at the weekend (and air/oil/etc), and a bottle of Forte here too.
The main thing will be to make it be less.. utterly hopeless at pulling away (honestly, it's worse than before!). If it were a petrol I'd suspect an air leak in the intake, but it's diesel so.. that wouldn't really matter. Hm.
this bit tends to split hence oil underneath.
Yes fill the filter with forte dont mix with diesel don't worry engine will start and run ok just give it a little throttle
Yes the manifold gaskets tend to wear out and draw in air they only cost £38.00ish to replace this will effect performance.
also clean out the small pipe thats under the manifold that leads to egr sensor this gets bunged up with oily crud