ISX oil leak

[Rawze]

Not saying this is your problem, but it is common ...

at a million+ miles, i would put my faith heavily into it being the cam bearings worn out, and the cam seals leaking behind the gear cover. -- just the first thing that comes to mind any ways, old heads that get worn out tend to leak behind the gear cover at the injector cam or valve cam as the bearings start showing copper.

Look for oil running down at the back of the gear cover where it meets the block just above the air-compressor. -- if it is wet there, then its a high possibility.

what usually comes next, if ignored long enough is a spun bearing in the head, Usually the one near the gear pump, where the engine brake harness connector is. If this happens, then you will loose the cam as well, sometimes rocker(s) too, and is a preventable couple thousand$$$ expense otherwise.