while i installed the 3"front2"back lift on my truck this past weekend i noticed a small black resevoir looking box next to the transmission under my truck. its about 3" by 3" by 2" plastic resevoir with a plug/washer that was loose and the box was empty. what is that, can someone help me out. i can't identify it in my haynes manual at all. thanks! i can't upload the photo, cause i guess im over my limit on attachments.