RD4 engine oil leak

Search this forum. There's been topics on this from others.
I've never had one of these engines apart but on most of the older Cat engines there's no seal only a reverse Buttress thread that pushed the oil back into a drain hole that goes back into the crankcase. You may want to check and see if the breather on the right side of the engine is clean. Could be too much crankcase pressure.

Thanks, I’m new to the forum and did find the search bar and the other posts. I’ve never tore apart any old diesel engines before, I mostly have gas v8 experience. This is my first dozer project. I checked the breather and it’s clean. If the drain hole is plugged would it cause a substantial oil leak? I can only run the machine for an hour or so before I need to add more oil. Is it possible to leak that much if the packing between the main cap and the block is shot?

Perhaps the main bearings are worn beyond spec and allowing too much oil for the reverse thread too handle.