What does it mean to have oil in my 2004 Discovery vacuum reservoir filter? Do I just replace it or is the problem elsewhere?

 

Where is the oil? Do you mean the coolant reserve jug? That would be head gasket.

 

This is part of the SAI system on top of the engine on the left-hand side,a black cylinder with a vacuum tube at each end.

 

I suggest you remove the intake tube and inspect the throttle body bore. If there is significant oil in there as well there is a good chance the oil seperator (I.E. PCV valve) is clogged. This creates pressure in the crankcase and pushes oil up through the breather tube into the intake manifold.

 

Thanks for the suggestion. I will try it out.