Anyone interested - if you visit the Port of Blyth website, you will see a map of Blyth Harbour, dated 1682, Seaton Sluice and Seaton Delaval, are spelled " Seatoun". So it looks like Seaton "Sluice" was already being used before the cutting of the 1800s.
Whilst on this subject of Seaton Sluice, I have an interest in a Bill Dent, (probably full name William) who originated from the Sluice. He would have been born about 1900, give or take a few years. He was in his 60s in the 1960s. He was a publican in Yorkshire, and the last pub he ran was in Pontefract. If earlier enquiries by me were correct, he died in Feb. 1993 in Pontefract.
If anyone has any knowledge of Bill, or family, I would be grateful for any information.