Mike - I have not been under the C12 in our coach. Thus I have not looked for the auxiliary transmission cooler. But I think it is located first inline from the door - streetside aft door behind the tag axle. It appears to be about the same length and 2/3rds the height of the engine cooling radiator. I took three pictures and the message above says the "attachments are now attached to this post." I guess we'll see if they are. They might need a good cleaning, eh?