Swapping someone else's turbo leads to a definitive answer as to what is at fault: the turbo or the engine?
TFS' turbo ain't exactly spanking new, but we know that it boosts up to 22psi with no problem whatsoever.
It doesn't smoke AT ALL, even after 10mins idle, and I only use "thin" Mobil1 0w40. No external leaks from the turbo whatsoever either.
BUT - the oil spots on my garage floor were replenished. AHA - at this stage (3rd turbo from AET!) it looks like the final leaks are not turbo-related. But where did they come from?
Exhaustive search showed that some of the leaks were coming from the oil return pipe sticking out from the LET sump (short block actually) I tried it (22mm) and it looked tight enough.
How tight should an oil return pipe be for crying out loud? Hold on .... according to TIS 55Nm! Most torque wrenches don't even cover this sort of force!
Mine was nowhere near as tight as that, no wonder it leaked (it actually looked as if the SUMP was leaking, but I knew it wasn't the case as I changed the sump gasket myself a couple of weeks ago)
55Nm people, and you need a deep 22mm socket as well. An O2 sensor socket also fits.
The oil return pipe on the (3rd) turbo was also a bit loose (also 22mm) and that should account for the upper bits of the leak)
I don't think you need to take the turbo off in order to tighten this pipe, it could be done in situ.
So...turbo owners with 'leaky sumps' try this first. You might just be lucky!