Sea-fever first line?

Does anyone have the originally published version of this poem by John Masefield? Searching the web shows at least two variations:

I must {go} down to the sea{s} again

and one the sites includes some discussion:
http://www.bartleby.com/103/98.html
(you should down about 1/3 of the way to see the post by T.P. Harvey) but no one mentions the original.

“The first line of ‘Sea Fever’ originally began, ‘I must go down.’ Twenty years later Masefield changed it to ‘I must down,’ but after twenty more years he put ‘go’ back. ‘Now, alas, I can’t make up my mind,’ he said.”

(from Best Remembered Poems, edited by Martin Gardner)

Plot thickens:
In this image from Salt-water Ballads, the line is “I must down to the seas again.”