Oil tracking though harness

I wonder if the oil is a red herring. When I bought my Td5 I was too busy checking for rust I forgot about checking the red plug. When I eventually checked it a month later it was swimming in oil and was leaking out into the seatbox. It ran like a dream though, well except for the leaking fuel pressure regulator.
Fitted a new injector loom, after sealing it up, and it's been fine, didn't take long for any residual oil to stop leaking through.