That thing sitting in the spring tower is the (secondary i believe) oil separator.

If you look closely, you see the primary oil separator by the firewall, and the upper portion of it vents to the lower separator which seems to just discharge into the engine bay.

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Vehicles:
2002 SLK 230
Gone but not forgotten:
1983 300D
1981 El Camino 'OILBRNR' - 6.2L diesel
OM617 powered '86 F150
1984 BMW 524td
2001 VW Beetle TDI
1994 Sunurban 4x4 6.5L diesel