The oily film in the top of my T-9 transmission has bugged me since I built the car. While I recently had the drivetrain out of the car, I decided to fix it once and for all. The car is vented through a small hole in the bump on the top cover. This hole is intentionally placed over the the reinforcing bracket that serves as the fulcrum for the upper selector rod. This is due to the swirl pattern of the lubricant when underway. This location allows the pressure to vent but a bit of oily vapor also escapes over time (probably why they built the cover with a lip all around it).

I welded on a steel AN-4 bung after drilling the correct diameter in the top over using the original vent hole as a pilot. I fabricated a 12" ss braided hose using a 90 degree fitting on the transmission end and a straight fitting on the other. This I simply bent 90 degrees and secured with a bracket near the rear of the engine (the minimum bend radius for -4 hose is 2"). I covered the end with an end cap that I had cross-drilled. After a couple of 30 minute runs in 80 degree weather yesterday, no residue was observed. Should I start to see evidence of lube at the vent, I can always extend it to a catch can.