If you need a new set...try Partman (Lighthouse Marine) in Riverhead Long Island, I don't think it will be that cheap though, they do deliver...I think they have them on their site for about $709....You might do better if you can source them locally, the shipping is expensive because they are heavy. In any case, you got a nearly new engine there that deserves a good exhaust system. Bad or not maintained exhaust is the #1 cause of inboard engine failure, with overheating and over-propping.
First, test them with acetone, then if they pass, get a price from an auto machine shop to make those mating surfaces look like new. Then, you might get 3 years on them before the next replacement. The only way around it would be to install full closed cooling and that will work only if the Volvo raw water pump can flow enough water to cool the manifolds too. Since they did not offer that as a factory option as far as I know, my guess is that they felt it safer to just cool the engine. Of course there are probably conversions to higher capacity impellers, with a through the hull pick up, that could be done, but it all costs money.
Yet another option for the future, is to see if you can convert over to the Merc dry joint exhaust system. This design totally separates the exhaust gas passage and the water cooling passage, so you don't have such a concern with leaky gaskets. They can still rust through though like any other cast iron manifold in salt water. I considered this when I did my top end overhaul last year but I wasn't sure if the Merc elbow angle/length would match up with the OMC/Volvo style Y pipe. And the dry joint design is more expensive even in aftermarket. Next time if I can get an exhaust shop to lend me a manifold and elbow for a day, I might try it out. I went with these (Volvo style) because I knew they would fit.
