I can't seem to find any information regarding gaskets for the heat riser. I have a large exhaust leak coming from the heat riser and when I removed it to inspect it seems there are no gaskets? The one end of the heat riser is flat and has a steel on steel seal to the manifold, and the other end of the heat riser has a machined donut shape that clamps to the pipe with the two bolts. None of these had gaskets and when I cleaned up the surfaces on the mating parts and reassembled the leak still happens. Is there supposed to be gaskets on both ends? Thanks