Benjamin looks to have left a will. From the National Probate Calendar (Index of Wills and Administrations):
Clayton, Benjamin of 14 Grove Road, Burnham-on-Sea, Somerset died on 28 May 1984. Adminstration Llandaff...
And as you found, you have the match in birth date of 27 Mar 1920 on his 1939 Register entry and death registration.
There is also a death reg and Will index entry for his wife Mary Edith who died 8 October 1985. Same address details, 14 Grove Road, Burnham-on-Sea, Somerset.
She was a little older than Benjamin. Her birth date on her death reg is showing as 29 May 1912.
As for Benjamin's history in Berlin, hopefully someone can advice further

Monica