So...
I've been battling with a chronic oil leak this week, originating from the turbo
At first I thought it was the oil return fitting because there was oil visible on the pipe feeding to the sump.
I pulled it off and the brass hose tail had begun to unscrew itself from the 10mm mild steel flange.
I bought a steel fitting, cut the hose tail end off and welded it to the flange to make a solid unit.
I thought the little puddle of engine oil when I parked was just residual oil that leaked onto the chassis and was dropping off when warm...wrong. The puddle size never got smaller
I searched all over for a possible source.
The oil feed fitting was fine, and I kept noticing the oil on the bottom of the turbo core cartridge.
My mind automatically went to worst case scenario, "What if the core is cracked ?!"
I plucked the turbo and downpipe tonight and started stripping the turbo down to see if the problem might be bad seals in the cartridge.
Everything looked fine, no oil anywhere.
When I went to loosen the 4 bolts in the cartridge that hold the compressor backing plate on, I didn't immediately click that they were very loose.
Only after I had all the bits laying on the work bench did I notice that there was oil on the outside of the o-ring seal side of the face that mounts up to the backing plate.
Turns out what had happened is I rebuilt the turbo and sent the cartridge to be balanced.
When it came back, I didn't check it before installing it.
the 4 bolts had worked themselves loose and slightly separated the cartridge just enough to allow oil to bypass the o-ring seal and push oil out of the threaded holes
I would never have found that leak if I hadn't stripped the turbo down.
Lesson learnt
Sorted it out and it's all back together now