I'm sorry, but I have no additional info on Benito Salas.
It has been years since I wandered the halls at the national Archives where the Old Army records are kept--and I understand much has changed.
But certainly you should begin with an effort (inquiry) to find Salas's service record (personnel file)--and also any pension materials. That he wrote to Winners of the West in late l934 suggests he may have followed pension legislation for vets of the frontier campaigns.
The Winners article indicates that he only served one enlistment, l880-85.

In my research I've found a fair number of instances where rules/regulatoins were bent, winked at or totally ignored in order to enlist (or re-enlist) a fellow with special and needed skills--such as a musician, craftsman, clerk/school teacher.

Switching gears: I'm always on the look out for good tales of the post-Civil WEar black regulars (aka Buffalo Soldiers). The pages of Winners of the West is a wonderful source. Sure some of the vets were writing long past the time of the events they "recalled"--and feded memory has to be factored im--but still the letters to Winners are authentic "voices" of therse soldiers.

Anyway, about good tales: here's a real beauty that recently came my way. So far I have nothing but what follows-but some day I would like to research this entire tale.
Here's the document:

Headquarters Department of the Missouri
Adjutant general's Office
Fort Leavenworth, Kansas March 23, l882

On the recommendation of their troop commander, and in consideration of gallant conduct in a fight with hostile Apache Indians, September l, l88l, Privates James Burton and James D. Phillips, of Troop I, 9th Cavalry, who were awaiting trial for desertion when they were released to participate in that fight, are restored to duty without trial, to date from September lst, l88l.

There may be the making of a movie in this tale--for big screen or TV.
And not that "Buffalo Soldiers" brand of crap of a few years back that had a black trooper played by Danny Glover shaking hands with an
Apache.

Tom Phillips