Hi Rob,
If you look at Eric's message just above this, and my reply to him, you will see all the census records where Mary Ann Brew's husband John Corkill was recorded as b. Maughold, so we need to find another marriage for your John C b.Marown. I can see how difficult it is with so many JC marriages in other parishes. It would be much easier for you if you were a descendant so that you could work your way backwards from known information.
I'm about to answer Eric's question about Corkill + Corkill marriages which will probably confuse everyone even further!
Sue