Sergio, who hails from Argentina, has a quite extensive collection of articles and images available on his websites about Royal Enfield and Panther, along with a Facebook page detailing numerous obscure but often very important marques such as Duzmo, ASL, Alegro, CRS (a French four), Galbusera, Praga, the Seal and Regal Green, some of which are shared on this site with English translations.
He also has fascinating pieces on radial engines (Megola et al), early forks and carburettors, an Australian V-Four which most Australians have never heard of, Borgo of piston fame...
Several pages are dedicated to the restoration of specific models of his own or his friends including Royal Enfield Model CO 1939, Model G 1949, Model J2 of 1948 and 1949.
His contributions to this site are prodigious. In addition to the numerous articles on rare, interesting, landmark and sometimes just plain quirky designs of yesteryear, the galleries contain images of machines displayed at motorcycle fairs in Buenos Aires and Rosario (his home town) and from the collections of museums and fellow enthusiasts.
Mention here must be made of Howard Burrows, who has aided and abetted Sergio in his research, and also Pierre Laumont who contributed information and images for the Eole V4 article.