I purchased replacement thermostats for my Mariner 150 (V6). I asked at the parts counter if there were any gaskets and they said no. Low an behold when I pulled the old ones out, they had rubber gaskets on them that fit around both the top and botom faces (a single piece).<br />Should I stetch them over the new ones or leave them off? It seems like the thermostats would be awfully sloppy in the housing without them, not to mention, I think the housings would leak if they were left off.