Disconnect the downpipe/exhaust flange, remove hoses from the turbo inlet
and outlet. The turbo is part of the exhaust manifold that bolts to the back
of the block. I think it's 6mm allen bolts that hold it on. Get it loose and
disconnect the oil feed lines, and vacuum line to the actuator.
Remove the whole assembly, others please feel free to chime in if I've missed something,
I've only ever done it once.
Put it on the bench and start studying, it's quite an amazing piece of engineering.
The exhaust drives the wheel that turns the shaft that drives the turbine
that compresses your intake air. The journal bearing between the 2 wheels is a
likely culprit for your oil leak. The turbocharger is the heart and soul of a TDI, it's how
you can make all that HP out of a little 4 cylinder.
The VNT mechanism, variable nozzle technology, adjusts the amount of
air that gets compressed, that's what the actuator controls.
This is a very basic explanation of what's going on, I'm no mechanic,
but until you get a handle on the turbo, how it works and what it's doing,
I suggest you won't make much progress with a TDI.
After that, injection of fuel, pistons and rings et al is pretty straightforward engine stuff.
The high pressure fuel pump is just that, a fuel pump, but operating, like
the engine compression, at much higher levels than a gasser.
The injectors have teeny tiny little nozzles that atomise the fuel, there is NO spark to ignite, just pressure.
Sorry to be so basic, but it took me a while to get a handle on how a diesel
works. Once the motor runs, the rest of the systems, transmission, brakes, etc are like any other car.
But pressures and tolerances on the key components of getting that motor going are very different to your normal gas engine.
I, and I'm sure others here, have used parts. Your turbo may well be in
pieces, I've got a couple old VNT15s for example. You may, or may not,
need one. At least on the bench you'll be able to give it a good clean,
check shaft play, and the condition of the vanes.
I gather your job needs you to get stuff going right away!
Unfortunately the bull in the china shop approach may have
you breaking stuff unnecessarily. A little more tortoise and a
little less hare in this case will get you there for less money and work.