If you paint the engine bay a semi gloss or flat black, it will NOT hide leaks. The leaks will be shiny, the paint will not be. I was going to suggest not painting the engine bay satin black for that reason, it looks like crap when it gets oil on it because it will show up shiny against the flat paint. But if you're worried about hiding leaks, well, satin black will not do that.
As for the rest of the car, paint it whatever you like. If the next owner gets tired of it, they can paint it. There's a really good chance when my Challenger gets painted it will be "hot rod" black- a nice satin black that's a little richer than flat black primer.
