Douglas O-2 Mail plane maintenance manual 1920’s?

Description

Found this in a used bookstore on my travels, Handbook of Instructions for Douglas O-2 Air Corps and US Air Mail.
19 pages on the old thick glossy type paper. Has some age yellowing on covers and pages, no writing anywhere. Staples have a bit of rust. Very light old paper smell have to sniff it to tell!
I cannot find a date, but I would guess from the 1920’s era.
Not sure what this is worth, I’ll let the auction determine or shoot me an offer!
5.00 media rate shipping in the US