Do you think all that smoke is from one cylinder? To me, it almost seems like oil is collecting on some flat surface, then the downhill angle is dumping it all into the intake. I don't notice much engine braking going down the hill, but I'll try shifting to N next time to see if it changes.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma