Hi Nick,
Very, very interesting. I know Gosbeck and have visited the old Post Mill remains there (built c1865; demolished c1925). There were two other mill site, one at The Grove, and another one lost in time; both of these were gone long before your uncle milled there, and were all wind driven.
I was however completely unaware of a watermill in Gosbeck! Do you have any other information? Was your uncle a Southgate, as George Southgate was the last miller at the postmill site.
I'd be most interested in any info you might have!
Cheers,
Windy