I have a Silver 66 with the exact same problem. I purchased it in March of this year along with a 3rd gen manifold and noticed the leak a couple months ago. I sent it to Industrial Injection for a rebuild. They said nothing was wrong with it but they rebuilt it and shipped it back. As soon as I put it back on the truck the leak was there 15 minutes later. I sent it back to Industrial because they were confused like me. After putting the 2nd rebuilt turbo back on the truck the leak was there again. Industrial Injection has been working with me trying to figure this out but no luck so far. They sent another drain tube and gasket for me to try and it did work for about an hour but the leak eventually returned. I'm clueless. Any help is greatly appreciated. Thanks