Its not leaking from the power steering somewhere and getting blown onto the side of the block?
Is it diesel? could be coming from the fuel return which comes out of the head on that side up near the front.
Other possibilities; The head itself, head gasket, rocker cover gasket, oil filler cap not sealing, PCV pipe has come loose. The head is slotted up against the housing for the timing chain, vacuum pump and injector pump, then there is a front cover in front of that. It could be leaking from any of those interfaces. The inlet manafold will have to come off minimum, allow about 4 hours for that fun job.
The pipe is the middle of the photo is the oil drain from the back of the head, it comes from the head as a metal pipe then goes to rubber before going into the sump.
The dip-stick tube is inserted in the sump and sealed with a simple o-ring down there.
Cheers,
FP