"failed either" is correct and usable in written English.
It is typically used to indicate that someone or something did not succeed in two or more possible options. Example: The team failed either because they were unprepared or because they underestimated their opponents.
Several times he failed either to hold on to shots or to shovel them clear of danger.
But the preponderance of the evidence suggests that the satellite failed either during the ascent or shortly afterwards".
Allison's research focussed on why T-cells failed either to recognize cancer as being aberrant or to attack it, as they do with microbes.
At the same time the Brothers inserted followers and allies wherever they could in state institutions.But the Brothers failed either to woo or to conquer the state.
To weed out incompetence, all officers in the Army had to pass an oral examination given by a board of experienced officers; those who failed either resigned or were stripped of their commissions.
Industry, starved of imported inputs and domestic investment and often mismanaged under state control, failed either to grow or to achieve acceptable standards of product quality or to remain commercially viable.
Later, as education minister, he faced down striking teachers but failed either to bring in much-needed reforms or prod his ministry into making efficient use of EU money.
But there was a mixed reception for new hosts James Franco and Anne Hathaway who, despite their early admission that they were in place in order to lure a younger demographic, failed either to sufficiently amuse or charm with their combination of big-toothed enthusiasm (Hathaway) and lo-fi smirking (Franco).
The great philologist E. A. Speiser, by contrast, whose 1962 translation of Genesis offered the best textual analysis of the time, failed either to see or to communicate this alarming vision of the deity when he had God telling Abraham "Do whatever Sarah tells you".
Up went an indulgence of over-inflated structures, a number of which have since failed either to find a worthwhile purpose (the Dome), or have lost their purpose (the Museum of Popular Music, Sheffield), or have simply failed on their own terms, like Clissold leisure centre.
But Bennett's reform measures aroused distrust in his own party and failed either to revive the public's enthusiasm or to counter its resentment over his previous laissez-faire policies, and in the October 1935 election he was overwhelmingly defeated by W.L. Mackenzie King and the Liberals.
