There are short and long versions of the oil separator part of the road-draft tube. The truck engines seem to have the long version. I believe the purpose of the "baffle" part of the tube is to condense oil vapor back into liquid then drain it back into the pan through a couple of internal holes. You can pry the cap off the fat part of the tube and see the baffle. I had OP's problem some years ago. I had not cleaned the breather when I rebuilt the engine. I took the breather apart. It was clogged with coke-like black stuff. The oil fumes were not condensing and just going out the road-draft tube condensing there and then onto the road, and the frame, and the transmission and everything else. I burned it out with a torch and cleaned out the drain holes, stuck the cap back on with some RTV silicone (not orange) repainted it and put it back on the engine. Problem solved.
