A manual may be downloaded from
Steve's Pages, a worthwhile endeavor.
I received mine, apparently made in 1940, with the recoil spring and guide reversed, the guide riding at the muzzle end of the frame. This eliminates the magazine disconnect function but otherwise has no effect I can detect. I reassembled mine correctly.
Given a gun that old and likely of unknown history, I think a spring set is in order. New springs certainly couldn't hurt. They are available at
Wolff Gunsprings
I considered mine for concealed carry, but rejected the idea because of the very poor sights. For a while I looked into installing better sights but did not find any I liked for the job. (I also found I am comfortable with a 1911, full sized or compact, making the 1903 a plinker.)
The little I have heard suggests that aftermarket magazines can be a problem, should only be purchased from folk who back them up.