The next option was to add a proper HKS cooler, but that is a big step. My objective and exceptions were minimal for the amount of work put into this - Lower the transmission temperature by a few degree F during normal driving and allow for quicker cool down during track time.
I have noted the results below.
In order to perform this modification, the rear diffuser needs to be removed. Removal is pretty straight forward.
Place chucks on both sides of a front wheel.
Jack up the rear of the GT-R, or jack up the front/middle of the GT-R and when the rear is high enough, place jack stands on the rear jacking point. One will do put if you want plenty of room to work the jacking up both will be good.
The rear bumper does not need to be removed for this.
Remove the 6 plastic fastener clips on the rear section of rear diffuser using a flat head screwdriver or removal tool.
Using a 10mm and 12 mm socket with appropriate extensions and a drive i.e. ratchet or impact remove the bolts mounting the rear diffuser to the body.
The LH and RH sections of the rear diffuser will stay attached to the car and literally hang around which is fine.
Once the diffuser is removed. Lay it on the ground. I fashioned a scoop using a sheet aluminum (doesn't rust, easy to bend, doesn't weigh much) picked up from a local hardware store for another project on my motorcycle.
After making a few measurements, cut the sheet out using some metal snips. Then worked the bends using a rubber mallet on a work bench. Smoothed any sharp edges using a file, then test fit it and kept bending it to get a good scooping angle, and coverage from the sides as well.
Before securing the pop rivets, decided to paint the scoop with a matte black paint and bake it in the oven for 10 minutes at 150F to cure up the paint. Finally secured the pop rivets.
Overall my personal non-empirical observations have been that the transmission takes longer 20-30 minutes more get to its highest peak for daily driving. For me this was 180-190F. What used to take 15-20 minutes now takes 30-40 minutes and what used to sit at 190F now sits at 181F. So about a 9F drop.
Also during track laps, the cool down from +220F to less than 200F now takes 1 lap versus 2 laps. Over the last 2 years, I have changed the angle of the scoop slightly to make the mouth opening slightly narrower than pictured, so that the air is forced to flow along the bottom of the transmission pan rather than be jammed up.
For the almost $0 it cost me to do this, I have to say it was worth it.
