So here is my final report on the M24 oil cooler. I was at the O'Fest at Barber and drove all sessions for 4 days and one session on the last day, which ended up being a bit over 300 miles on the track. Temps during the week were in the high 60s to as high on Saturday in the low 80s. I still think for my application that this oil cooler is a valuable addition. However, in regard to oil temperature reduction, I can't really reach any conclusion.
I suspect that the stock oil temperature gauge can't really show a difference of 18-20F. During my track sessions I could still get the needle up to the middle mark between the 210 and 300F marker on the gauge. One thing that seems to be pretty clear is that the temperature recovery is much quicker than stock. In one cool down lap (2.2 miles) I could get the temp to come down to just over 210F before track exit. I've never seen this quick a cool down even when running in 50 degree weather. So unless you have a really accurate aftermarket oil temp gauge I don't think you'll see a difference based on the stock gauge. Otherwise, no issues with the oil cooler and it's a nice piece of fabrication.