Thanks for the tip Jay, I recently had a close look at the turbo, there is no shaft play at all, vertical or lateral, yet I'm getting a small amount of oil out of the turbo outlet pipe when I hold the engine at about 2500 revs. The crankcase ventilation system was disconnected when I did this test, so the oil has to be coming from the turbo compressor shaft, which is strange for a turbo thats in such good nick, and it's also a water cooled turbo on a diesel engine which should keep shaft/bearing/seal temperatures down to a safe level! Excessive oil pressure/flow is the most likely culprit here, but I'm open to other views!