I am replacing my impeller on my MC-1 outdrive and noticed there is no gasket for the halfs. Should I just put everything back together or skim coat some silicone?
Sounds like you need to do just a tad bit more research and look at your instructions / installation guide. It will show you the required o-ring that seals the two halves. Did you see an o-ring (actually called a "quad ring) when you took it apart?