I've just fixed this on my 110 as well, mine split on one of the Bends of the pressure line. A combination of a compression fitting and some rubber hose sorted the leak, we then ran into the stupidity of land rovers not easily obtained fittings for the pump so I ended up Lathing up a new banjo fitting to take ⅜BSP fittings. If the pipe goes again we can just make up a new rubber in 5 minutes.
I've milled loads of brake pads, did a set just last week.
Its abrasive to even carbide cutters so they dont last long. Wear a mask and be prepaired to be covered in more dirt and snot than after a day of machining cast iron.
To me, this has got to be something wrong in the injection pump, your Variable Geometry Turbo will create boost at lower RPM hence the issue clears sooner with it.
I'm not keeping up with this as well as I could, are you getting all the same issues if your running a Standard turbo, I'm working if the Vanes in the turbo are sticking when the engine is switched off due to bad adjustment off the actuator and there needing a bit of a shove to get them moving, then they only get stuck again when you switch the engine off.
Is it an air related problem? Smoke suggests not enough air. Something often miss understood is that Boost pressure doesn't necessarily mean you've got enough volume of air.... If you have the boost pressure then your injection pump will fuel for it, but you might not have enough flow to actually ha e enough air to burn all that fuel.
Yes your just being thick. 😉
My down pipe on my 200TDi is clamped on with a Mikalor clamp which works a charm and is much nicer than the D clamp you speak of.
If the oil pressure issue from cold is on a 300TDi, I would suggest the timing case is worn around the oil pump. The design of the 300 oil pump is Gash at best.
To do it properly it's taken the whole pump apart, where it's leaking is basically the first bit with a seal on to go into the pump. Given the cleanliness required you want the pump off and on a bench. A few have stretched the ring over the housing into its groove by carefully pulling the rear housing out. Personally I don't see why you would get an O ring, knacker it like that during fitting and think it was agood idea.