LB7 Oil Smoke Exhaust and Oil leak - Help Plse

My 04 DM LB7 with 90K miles blew about 3 miles worth of blue gray oil burning smoke through the exhaust and has engine oil dripping from the rear mail seal area i.e the connection right behind the oil pan. Here’s what happened.

I had to move the 5th wheel in the yard and decided to go around the block to try out my new Prodigy brake controller. Engine was already warm. About a mile down the road I have a huge amount of oil burning exhaust. Gauges and running noises are normal. I stopped, turned off the engine as there was so much smoke I thought something might be on fire. With the engine off the smoking stopped so it wasn’t coming mainly from oil on the exhaust.

I started up again and had clouds of smoke and headed home. The smoking ended just before I got home. Checked the engine bay-no oil or obvious faults anywhere top side. Oil level was down a part a quart. Unhooked the trailer, drove forward and noticed numerous fairly heavy oil streaks in a wide pattern on the ground.
Underneath the truck the engine oil was dripping from the RMS seal area and had blown all over the transmission etc But the curious thing is that there is engine oil all over the passenger side of the engine.

Checked the oil again and ran the truck into my mechanic. There was no more exhaust smoke. He had just installed a secondary fuel filter the day before and changed the primary filter and said the area was bone dry as was the RMS seal area. Now the RHS of the engine looks like a quart of oil was sprayed on it.

It looks like a blown RMS except for all the oil on the side of the engine and the large amount of oil that went through the engine or the just the exhaust. My mechanic doesn’t think either should happen with RMS failure.
The truck is sitting at the shop waiting for Monday morning. I’d appreciate opinions on whether it is RMS or where to look for another culprit/ thanks for your help.

From your description, I would doubt a main seal leak. Unheard of with the Duramax, and don't develop, then go away, as you've described...

My question is during the oil burning even - how sure are you that the oil smoke was coming from the exhaust, rather than just from under the truck? From the sounds of your engine bay, I'd imagine you had oil burning off the passenger side exhaust manifold, which would lead me to the assumption that you have an oil line or fitting leaking somewhere...

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Originally Posted by Mark Rinker

From your description, I would doubt a main seal leak. Unheard of with the Duramax, and don't develop, then go away, as you've described...

My question is during the oil burning even - how sure are you that the oil smoke was coming from the exhaust, rather than just from under the truck? From the sounds of your engine bay, I'd imagine you had oil burning off the passenger side exhaust manifold, which would lead me to the assumption that you have an oil line or fitting leaking somewhere...

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That's good news on the RMS-only the smoky exhaust went away-Oil leak continues the drip but not known from where-drips off engine at RMS but suspicion is turbo.

Smokey exhaust was pouring out of the exhaust pipe-could see it in the rear view mirror and also when I stopped to looked. When I cut engine, smoke stopped.

Yes I'm hoping that mechanic working on the secondary fuel filter install loosened, moved, strained something that was in the way-he was working in that area of the engine bay--of course on Fri pm at quitting time he was just looking at the RMS and even though the oil spray on the RHS might have pointed in his direction, he wasn't talking about that likelihood.

Best case is that he just loosend or broke something-other wise could be turbo lines, seal or?