I have found the After Market manifolds to be junk. I'm not talking about CMI or Stainless Marine or anything like that. I mean the aftermarket cast iron replacements like Osco. The gasket surfaces are not near as wide as stock ones and they quickly corrode and allow water intrusion through the elbow gaskey surface. I know they are alot cheaper but they just don't hold up. You can get a pair of aluminum manifolds from Eddie Marine in California for it that are made by a company called Red Line. They preform pretty well. When you get them they are raw aluminum though and still have all the casting flash and dimples on the outside. A little polishing and then powder coating or anodizing and they look great.