Clean the hose and turbo inlet, direct the vent hose into any old bottle, cap the fitting in the big hose, go for a spirited drive. See if there's any/more oil in the turbo inlet or in the bottle.

Before anything else, takes lots of pictures of the engine bay as it is. Take close-ups of wiring harnesses and connectors, the fuel supply and return lines by the big filter, etc.

Sixto
87 300D