Compare it to the pictures here: http://varietyvista.com/02a LC RPMs Vol 1/RPMs 1938S.htm It does not appear to match any of the pictures listed. It may be a new vareity, it may be a die chip, or it may be that your pictures aren't showing the RPM well. For any authoritative response, send it to James Wiles and he'll confirm it's one.
I considered this as well (using Wexler's), but the mintmark position appeared to be somewhat lower on the OP example. Perhaps it's just the angle and/or lighting?
Here's an animation between the OP's image and one of my own of a 38-S RPM#2. Keep in mind that the OP coin is worn and shows damage and hits, so some features are a bit distorted, but the serif to the West is pretty compelling. Some other features of the MM seem to show a bit as well.
You make a rather compelling case, and the animation is much preferable to flipping from one image to another (on a phone) trying to compare the exact location. Thank you.