I've had a bad leak on my OM617 Turbo powered 300TD, bad enough that I couldn't really tell where it was coming from because over time the whole undercarriage was coated with oil. I had a local shop steam clean the undercarriage so I could hopefully identify where it was coming from (my fear is that it would turn out to be the rear main seal).

The shop did a great job cleaning everything off so i had a good baseline to start observing where it was leaking. After one ~30min drive (mixed street and freeway) there was already oil dripping off of the support bar. Looking at the engine from the top I noticed that the top of the sump was covered in a puddle of oil.

My assumption here is that the turbo drain seals are causing the problem, but looking at the turbo drain tube I don't see any oil on the tube itself, i.e. it doesn't appear to be leaking from the top.

My next assumption is that the seals at the bottom of the tube (the ring seal in the sump and/or the grommet at the top of the sump) are failing, but would failure of one or both of these result in a large amount of oil leaking?

I would have expected a large amount if the top of the oil drain tube was leaking, but how does failure at the bottom result in such a large amount of oil leaked? Is there enough pressure in the sump that while driving oil is pushed out of the drain tube opening?

Or are there other leak causes I am not considering here? I think the smaller drain from the air cleaner has a check valve in it. What happens if that check valve fails, can it result in leaks?