Web references to the 1951 senior Manx TT say Geoff Duke was the winner. I have some newspaper clippings which attribute the win to D E Bennett, Bennett also broke Dukes existing lap record.

The race was postponed from the previous day due to weather and Geoff Duke was not even entered as he was getting married. Duke went on to be world Champion, Dave Bennett died in the Swiss Grand Prix the following year (1952) racing for Norton colours

Can anybody verify this?