Crankcase fumes

[Lonestar10]

Every time I use my engine brake to slow down I get an overwhelming crankcase smell in the cab no other time I can full throttle this thing with the wind coming from any direction and nothing only when using the engine brake and it's gotten worse now that it's warmed up.

I put a plug on end of my exhaust manifold in case it was from the crossover and no change which granted would smell like exhaust not crankcase.

I have a new head and valve stems look good so seals are doin their job.

Crank vent tube when it was cold out with turbo at 85% closed 1500rpm was basically like a nice hot cup of coffee for steam coming out.

Tuned so no crank pressure sensor to look at driving and my only oil leak is from Jake brake plugin on side of head.

Never add any oil in 15,000 mile oil changes within first 5-7k miles it usually gets about half way through hash marks on dipstick then never moved again till it's changed.

What am I missing as far as what to look at.