Someone correct me if I am wrong but also a reason not to put a tranny cooler on a manual is because an automatic has a pump that circulates the fluid around and thus through the tranny cooler whereas a manual does not.

 

That about sums it up, lol.

There's no pump to circulate the fluid to cool it down anyway... But as long as you have the right fluid in there, it's not going to cause a problem... Though, maybe having a little bit heavier fluid might help out if you're doing a lot of towing, I guess...