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?

Hi Nigel I think you are getting confused between the Manx Grand Prix and the TT (2 separate meetings). Geoff Duke won the senior TT in 1951 whilst D.E. Bennett won the senior Manx Grand Prix.
Hope this helps. Steve

Interesting that the last finisher took 3 hours 50 minutes, over an hour longer than Geoff Duke.
Wouldn't they be flagged off nowadays?

Nigel, Dave Bennett did indeed break Geoff Duke's 1949 MGP senior lap record of 87.48mph with a new speed of 89.75mph or 25 min 45sec.
This was from Bill Snellings and Peter Kneale's book "The History of the Manx Grand Prix 1923 - 1998". There is a link on this site to Amulree Publications.

Spent Friday afternoon in the company of 1946 Senior winner,Ernie Lyons at his County Kildare home, what a welcome we had & what delightful people Ernie & his wife.He is 90 next week and the memory and humour are as sharp as ever.