Might be Peruvian. Without a crest Argentine was my first guess but I think you are correct on DWM manufacture of the Argentine. Also that answers the Original Mauser question. It has the high clip hump so I'd guess the crest was scrubbed.

The plot thickens. I know that the models with the "roller coaster" rear sight were very common after WWI but where a 1909 rifle would show up is beyond me unless it wasn't delivered. I simply don't have the depth of knowledge to know that.

Research here I come.